Court Opinion

ID: 4185170
Source: CourtListenerOpinion
Date Created: 2017-07-11 17:09:51.997938+00
Date Added: 2024-06-11T14:39:40.107373
License: Public Domain

Stewart Levitas v. Michael Davon Christian, No. 58, September Term, 2016, Opinion by
Adkins, J.

MARYLAND RULE 5-702 — EXPERT WITNESS TESTIMONY — SOURCE OF
LEAD EXPOSURE: In a lead paint case, a pediatrician who was designated as an expert
witness had a sufficient factual basis under Maryland Rule 5-702 to testify about the source
of the plaintiff’s lead exposure. The expert considered information given to him by the
plaintiff’s attorney, which included positive lead testing on the subject property, the age of
the property, Maryland Department of the Environment and Department of Housing and
Community Development records, the plaintiff’s Department of Health and Mental
Hygiene testing records, and family members’ deposition testimony, and explained how he
assessed this information. Additionally, the expert took into account the other possible
source of the plaintiff’s lead exposure when developing his opinion. Thus, the trial court
abused its discretion in precluding him from testifying about source causation on the
ground that his opinion lacked an adequate factual basis.

MARYLAND RULE 5-702 — EXPERT WITNESS TESTIMONY — MEDICAL
CAUSATION: In a lead paint case, a pediatrician who was designated as an expert
witness had the requisite qualifications and factual basis under Maryland Rule 5-702 to
testify about the nature and extent of the plaintiff’s lead-caused injuries. Because the expert
was experienced in treating lead-poisoned children and familiar with current lead-
poisoning research and the IQ test used to assess the plaintiff, he was qualified to testify.
A neuropsychologist’s report, medical records, and other information regarding the
plaintiff and the properties he lived at as a child were an adequate factual basis for the
expert to opine about the cause of the plaintiff’s cognitive impairments. Additionally, a
study on IQ loss in lead-poisoned children provided a sufficient factual basis for the expert
to testify about the plaintiff’s IQ loss. Thus, the trial court abused its discretion in
precluding the expert from testifying about medical causation on the grounds that he was
not qualified and his opinion lacked an adequate factual basis.
Circuit Court for Baltimore City
Case No.: 24-C-11-000954
Argued: February 6, 2017
                                   IN THE COURT OF APPEALS

                                        OF MARYLAND

                                              No. 58

                                      September Term, 2016

                                       STEWART LEVITAS

                                                v.

                                   MICHAEL DAVON CHRISTIAN

                                       Barbera, C.J.
                                       Greene
                                       Adkins
                                       McDonald
                                       Watts
                                       Getty
                                       Battaglia, Lynne A. (Senior Judge,
                                        Specially Assigned),

                                              JJ.

                                       Opinion by Adkins, J.
                                        Getty, J., dissents.

                                       Filed: July 11, 2017
       Issues about an expert’s qualifications and foundation for his opinion are no

strangers to appellate courts, and the complex issues of causation in lead paint cases

generally require expert testimony, which is often challenged. Today we review a case in

which the trial court excluded the plaintiff’s expert witness—a ruling fatal to his claim.

We consider whether it erred in doing so.

                         FACTS AND LEGAL PROCEEDINGS

       Respondent Michael Christian was born on February 12, 1990. From his birth until

October 1992, he resided with his mother, Nickolas Skinner (“Nickolas”), and

grandmother, Betty Skinner (“Betty”),1 at 3605 Spaulding Avenue (“Spaulding”) in

Baltimore City.2      Christian and his mother then moved to 4946 Denmore Avenue

(“Denmore”) in October 1992, where they resided for almost a year. In September 1993,

Christian and his mother moved back to Spaulding and lived there for another four years,

until September 1997.

       Christian’s blood was tested eight times between November 1990 and October

1993. In April 1991, he exhibited an elevated free erythrocyte protoporphyrin (“FEP”)

level, which does not measure a child’s blood lead level but is an initial screening test for

lead exposure. From February 1992 to October 1993, Christian displayed elevated blood

lead levels five times as follows:

       1
           We use the Skinners’ first names to avoid confusion. We mean no disrespect.
       2
        Respondent Michael Christian’s grandmother, Betty Skinner (“Betty”), leased
3605 Spaulding Avenue (“Spaulding”) beginning in 1989. As of the date of her deposition
on March 21, 2013, she still lived there.
                                                                     Christian’s
              Date Taken              Blood Lead Level3
                                                                      Address4
           February 20, 1992                9 μg/dL                   Spaulding

           February 18, 1993                10 μg/dL                  Denmore

              July 16, 1993                 17 μg/dL                  Denmore

           September 2, 1993                12 μg/dL                  Denmore

            October 6, 1993                 14 μg/dL                  Spaulding

      In 2011, Christian filed suit in the Circuit Court for Baltimore City against Petitioner

Stewart Levitas, the owner of Spaulding when he lived there, alleging negligence and

violations of the Maryland Consumer Protection Act.5              In February 2012, Arc

Environmental, Inc. (“Arc”) tested the interior and exterior of Spaulding for lead using x-

      3
        Blood lead levels are measured in micrograms per deciliter (μg/dL) of blood. See
Standard Surveillance Definitions and Classifications, Centers for Disease Control and
Prevention, https://www.cdc.gov/nceh/lead/data/definitions.htm (last updated Nov. 18,
2016) [https://perma.cc/K4A8-ZDKG]. As of 2012, the Centers for Disease Control and
Prevention considers blood lead levels greater than 5 μg/dL to be elevated. Id.
      4
          We used the addresses and dates listed in Christian’s Answers to Levitas’s
Interrogatories and Nickolas’s deposition testimony as opposed to the addresses on the
Maryland Department of Health and Mental Hygiene (“DHMH”) lab reports because this
is the residential history Christian’s expert witness, Howard Klein, M.D., relied on when
developing his lead source opinion. If we were to use the addresses on the DHMH lab
reports, more of the reported elevated lead levels would correspond to his residence at
Spaulding than at 4946 Denmore Avenue (“Denmore”). According to the lab reports,
Christian lived at Denmore for the lead level reported on February 20, 1992 and lived at
Spaulding for the three lead levels reported on February 18, July 16, and September 2,
1993.
      5
        Christian also sued the owners of Denmore. His claims against them were
dismissed with prejudice.

                                             2
ray fluorescence testing. Arc summarized its findings in a report for Christian (“Arc

Report”). Thirty-one interior surfaces and five exterior surfaces tested positive for lead.

The lead-positive interior surfaces included door jambs, baseboards, and window sills,

casings, and sashes. Exterior window sashes, casings, and door jambs also tested positive

for lead.

       During discovery, Christian designated Howard Klein, M.D., a pediatrician with

experience treating lead-poisoned children, as an expert witness who would opine on the

source of Christian’s lead exposure—source causation—and his lead-caused injuries—

medical causation. As to the source of Christian’s lead exposure, Dr. Klein testified in his

deposition that he was “of the opinion that [Christian] was exposed to lead-based paint” at

Spaulding. The basis for his opinion was: (1) the age of Spaulding—built in 1944; (2) the

Arc Report; (3) a Maryland Department of the Environment (“MDE”) certification

reflecting that the property was not lead free; (4) a Department of Housing and Community

Development (“DHCD”) violation that detailed the poor condition of the property; (5)

Christian’s elevated FEP and blood lead levels while he was living at Spaulding and

Denmore; (6) Betty’s and Nickolas’s deposition testimony that Spaulding was in disrepair

while Christian lived there; (7) Nickolas’s testimony that she saw Christian touch areas

where paint was peeling around the windowsills at Spaulding; and (8) Nickolas’s testimony

that Christian stayed at Spaulding under the supervision of family members while she was

at work during the day, both while they were living at Spaulding and while they were living

at Denmore. Dr. Klein further testified that these facts establish that “there was lead-based

                                             3
paint [at Spaulding].” Finally, he acknowledged that Denmore was also a source of

Christian’s lead exposure.

       In his expert report on medical causation, Dr. Klein concluded “within [a]

reasonable degree of medical certainty” that lead caused Christian’s mental retardation,

impaired cognition, and learning disabilities. He further opined in his deposition that as a

result of Christian’s exposure to lead, he lost 7.4 to 9.4 IQ points. Dr. Klein based his

opinion on: (1) a neuropsychological evaluation of Christian by Barry Hurwitz, Ph.D.; (2)

Christian’s medical records; (3) Christian’s Answers to Interrogatories; (4) information on

Spaulding and Denmore; (5) Christian’s Maryland Department of Health and Mental

Hygiene (“DHMH”) lead testing records; (6) MDE records; (7) DHCD records; and (8)

Christian’s school records. To calculate Christian’s IQ loss, he relied on the Lanphear

study,6 which found that children with certain average lifetime blood lead levels lost a

specific number of IQ points. Dr. Klein averaged Christian’s blood lead levels and then

determined his loss in IQ points based on the study’s results.

       Levitas filed a motion to exclude Dr. Klein from testifying about source causation

on the grounds that he lacked both the necessary qualifications and a sufficient factual basis

for his opinion.7 Levitas also moved for summary judgment in his favor if Dr. Klein were

excluded.

       Richard L. Canfield et al., Intellectual Impairment in Children with Blood Lead
       6

Concentrations Below 10 μg per Deciliter, 348 New Eng. J. of Med. 1517 (2003).
       7
         Levitas also moved to exclude the Arc Environmental, Inc. test results (“Arc
Report”) and “any testimony related thereto.” The Circuit Court for Baltimore City denied
this motion. Levitas has not appealed that decision.

                                              4
       On July 10, 2013, the Circuit Court held a hearing on Levitas’s motion to exclude

Dr. Klein. At the hearing, Levitas argued that Dr. Klein should be precluded from

testifying about both source causation and medical causation. Ruling from the bench, the

hearing judge excluded Dr. Klein’s testimony on both of these topics. The court reasoned

that Dr. Klein should be prevented from testifying about the source of Christian’s lead

exposure because “he did not, or had very little . . . information concerning other sources

[of lead exposure].”8 It also precluded Dr. Klein from testifying about the cause and extent

of Christian’s injuries because he was not qualified and his opinion lacked a sufficient

factual basis under Maryland Rule 5-702. As to his qualifications, the court reasoned that

Dr. Klein would not be able to explain the IQ test results to the jury because he does not

use the test in his own practice. As to his factual basis, the court explained that Dr. Klein

relied on information from Dr. Hurwitz and Christian’s attorney in developing his opinion,

rather than examining Christian himself, which was not sufficient. The Circuit Court

declined to grant Levitas’s motion for summary judgment, however, because the Arc

Report was “direct evidence” of lead at Spaulding.

       On August 20, 2013, the Circuit Court entered a written order precluding Dr. Klein

from offering expert opinions on “source, IQ loss, alleged injuries due to lead, or other

causation issues.”9 For the purposes of appealing the Circuit Court’s decision to exclude

       8
         The Circuit Court excluded Dr. Howard Klein’s lead-source causation testimony
because he lacked a sufficient factual basis for his opinion, not because he was not qualified
to offer an opinion on the subject.
       9
         When the Circuit Court’s written order was entered, it erroneously denied
Levitas’s motion to exclude Dr. Klein. Levitas timely filed a motion for reconsideration,

                                              5
Dr. Klein, the parties agreed that without Dr. Klein’s testimony, Christian could not make

out a prima facie case of negligence because he could not establish medical causation.

Therefore, the parties requested that the Circuit Court enter summary judgment in Levitas’s

favor to allow Christian to appeal the expert’s exclusion.10 The court granted the request,

and Christian appealed.

       In the first of two Court of Special Appeals opinions, the intermediate appellate

court affirmed the Circuit Court’s decision to exclude Dr. Klein. Christian appealed to this

Court, and we, in a per curiam order, vacated the judgment and remanded the case for

reconsideration in light of Roy v. Dackman, 445 Md. 23 (2015), reconsideration granted,

(Nov. 24, 2015). Christian v. Levitas, 445 Md. 240 (2015). On remand, the Court of

Special Appeals, in an unreported opinion, reversed the Circuit Court’s decision to exclude

Dr. Klein. Christian v. Levitas, 2016 WL 4076100, at *6 (Md. Ct. Spec. App. Aug. 1,

2016). It concluded that Dr. Klein was qualified and had a sufficient factual basis to opine

that Christian was exposed to lead at Spaulding and that lead caused his injuries. Id. at *4–

*5. Levitas appealed.

       We granted certiorari to answer the following questions:11

requesting that the court amend the order to reflect its ruling from the bench. The court
granted Levitas’s motion.
       10
          The parties entered into an agreement which provided that “[Christian] intends to
appeal the order(s) excluding Dr. Klein’s testimony, arguing . . . that [he] is qualified to
offer testimony as to the source and cause of [Christian]’s injuries due to lead ingestion,
and also that Dr. Klein had a sufficient factual basis for his testimony.”
       11
         We have rephrased the two questions presented in Levitas’s Petition for a Writ of
Certiorari. His Petition included the following questions:

                                             6
              1. Did the trial court err in excluding Dr. Klein’s testimony
                 regarding lead-source causation?

              2. Did the trial court err in excluding Dr. Klein’s testimony
                 regarding medical causation?

       Because we answer these questions in the affirmative, we shall affirm the judgment

of the Court of Special Appeals.

                               STANDARD OF REVIEW

       It is often said that decisions to admit or exclude expert testimony fall squarely

within the discretion of the trial court. See, e.g., Bryant v. State, 393 Md. 196, 203 (2006)

(collecting cases). A discretionary ruling, however, is not boundless and must be tethered

to reason. We have explained that an abuse of discretion is “discretion manifestly

unreasonable, or exercised on untenable grounds, or for untenable reasons.”

Neustadter v. Holy Cross Hosp. of Silver Spring, Inc., 418 Md. 231, 241 (2011) (emphasis

added) (quoting Touzeau v. Deffinbaugh, 394 Md. 654, 669 (2006)). Appellate courts will

not affirm a trial court’s discretionary rulings “when the judge has resolved the issue on

              1. Whether the Court of Special Appeals erred in
                 reconsidering all issues in this case when this Court’s order
                 for “reconsideration in light of Roy [v. Dackman, 445 Md.
                 23 (2015), reconsideration granted, (Nov. 24, 2015),]”
                 should have only impacted the issue of expert
                 qualifications.

              2. Whether the trial court abused its discretion in excluding
                 Dr. Klein’s testimony where the record showed that Dr.
                 Klein did not have a sufficient factual basis to support either
                 his opinion as to the source of lead exposure or the cause
                 and extent of Mr. Christian’s alleged injuries.

                                              7
unreasonable or untenable grounds.”12 Id. (internal quotation marks omitted). Such

grounds include “when a trial judge exercises discretion in an arbitrary or capricious

manner or when he or she acts beyond the letter or reason of the law.” Garg v. Garg, 393

Md. 225, 238 (2006) (citation omitted). The trial court must apply the correct legal

standard and “a failure to consider the proper legal standard in reaching a decision

constitutes an abuse of discretion.” Neustadter, 418 Md. at 242 (emphasis added).

       Below we examine the Circuit Court’s rationale for excluding a crucial expert

witness to assess whether it abused its discretion.

                                      DISCUSSION

       Levitas contends that the Circuit Court correctly excluded most of Dr. Klein’s

testimony because he lacked a sufficient factual basis to opine about the source of

       12
          Not all evidentiary rulings are reviewed for an abuse of discretion. Judge
McDonald, writing for the Court, explained the applicable standards of review for these
rulings in Mathews v. Cassidy Turley Maryland, Inc., 435 Md. 584 (2013):

                     Some matters, such as the weighing of the relevance of
              proffered evidence as against unfair prejudice or other
              considerations, are left to the “sound discretion” of the trial
              court. Such decisions will be reversed only for abuse of
              discretion. Other evidentiary rulings are based on a “pure legal
              question.” In those circumstances, an appellate court considers
              the legal question without deference to the decision of the trial
              court.

Id. at 599 (citations omitted). In that case, we reviewed de novo the trial court’s decision
to exclude a bank examiner’s report on the grounds that it was inadmissible hearsay. Id. at
628–32.

                                              8
Christian’s lead exposure and the nature and extent his injuries related to such exposure.13

Christian flatly disagrees.

       Expert testimony is meant to assist the jury in resolving an issue outside the average

person’s realm of knowledge. Roy, 445 Md. at 41 (citing Radman v. Harold, 279 Md. 167,

169 (1977)). Under Maryland Rule 5-702, expert testimony “may be admitted, in the form

of an opinion or otherwise, if the court determines that the testimony will assist the trier of

fact to understand the evidence or to determine a fact in issue.” The court bases this

determination on three factors: “(1) whether the witness is qualified as an expert by

knowledge, skill, experience, training, or education[;] (2) the appropriateness of the expert

testimony on the particular subject[;] and (3) whether a sufficient factual basis exists to

support the expert testimony.” Md. Rule 5-702.14

       13
            Levitas also argues that the Court of Special Appeals should have only
reconsidered Dr. Klein’s qualifications, and not the factual basis for his testimony.
Specifically, Levitas contends that Roy “did not evaluate the factual basis underpinning the
expert’s opinions,” and therefore it has no bearing on the outcome of this case. Levitas
misreads Roy. The Court found the plaintiff’s expert, Eric Sundel, M.D., competent to
testify about the plaintiff’s injuries based on his “academic and experiential qualifications”
and the materials he relied on. Id. at 49–52. We held that Dr. Sundel was not competent
to testify, however, regarding the source of the plaintiff’s lead exposure because he lacked
a sufficient factual basis. His opinion was “based solely on scant circumstantial evidence,
including the age of the home and exterior tests of the paint on the dwelling at [the subject
property].” Roy, 445 Md. at 47. Because our order instructed the Court of Special Appeals
to reconsider its opinion “in light of Roy,” without further instruction to confine its analysis
to Dr. Klein’s qualifications under 5-702(1), it was proper, on remand, for it to include
consideration of the factual basis for Dr. Klein’s source testimony.
       14
          This case implicates the first and third factors, although our discussion reverses
that order.

                                               9
       We have repeatedly explained that an expert may be qualified to testify if he “is

reasonably familiar with the subject under investigation.” Roy, 455 Md. at 41 (emphasis

added) (quoting Radman, 279 Md. at 169). This familiarity can come from “professional

training, observation, actual experience, or any combination of these factors.” Radman,

279 Md. at 169. An expert, therefore, does not need to have hands-on experience with the

subject about which he proposes to testify. Id. at 170–71 (citations omitted). The often-

cited illustration of this concept is a law professor who is an expert in trial procedure even

though she has never tried a case. Id. at 171 (citation omitted). Similarly, a doctor may be

qualified to testify as a medical expert even though she does not have experience with a

particular procedure or area of specialization. Id.

       An expert’s testimony is admitted “because it is based on his special knowledge

derived not only from his own experience, but also from the experiments and reasoning of

others, communicated by personal association or through books or other sources.” Id. at

170 (citation omitted). “It is sufficient if the court is satisfied that the expert has in some

way gained such experience in the matter as would entitle his evidence to credit.” Id. at

169 (citation omitted). A trial court may not exclude an expert if “his reading can be

assumed to constitute part of his general knowledge adequate to enable him to form a

reasonable opinion of his own.” Id. at 170 (citation omitted).

       Expert testimony must also have an adequate factual basis so that it is “more than

mere speculation or conjecture.” Exxon Mobil Corp. v. Ford, 433 Md. 426, 478, as

supplemented on denial of reconsideration, 433 Md. 493 (2013) (citation omitted). If an

expert’s conclusions are not supported by an adequate factual basis, his opinion has no

                                              10
probative force. Beatty v. Trailmaster Prod., Inc., 330 Md. 726, 741 (1993) (citation

omitted). The probative value of an expert’s testimony is directly related to the “soundness

of [the] reasons given” for his conclusions. Id. (citation omitted). An adequate factual

basis requires: (1) an adequate supply of data; and (2) a reliable methodology for analyzing

the data. Roy, 445 Md. at 42–43 (citation omitted); Ford, 433 Md. at 478 (citation omitted).

In addition, if the facts and data that an expert relies on are “of a type reasonably relied

upon by experts in the particular field in forming opinions or inferences upon the subject,”

they need not be independently admissible at trial. Md. Rule 5-703(a).

       In assessing the expert-witness factors, the trial court is only concerned with

whether the expert’s testimony is admissible. “[O]bjections attacking an expert’s training,

expertise or basis of knowledge go to the weight of the evidence and not its admissibility.”

Baltimore Gas & Elec. Co. v. Flippo, 112 Md. App. 75, 98 (1996), aff’d, 348 Md. 680

(1998) (citation omitted). An expert’s qualifications and methods may be teased out during

cross-examination, and the jury can then assess how much weight to give his testimony.

Roy, 445 Md. at 43. “Even if a witness is qualified as an expert, the fact finder need not

accept the expert’s opinion.” Walker v. Grow, 170 Md. App. 255, 275 (2006).

                                 Lead-Source Causation

       The third factor in Rule 5-702—“sufficient factual basis”—garners the most debate

between the parties. The Circuit Court restricted Dr. Klein’s testimony on the ground that

he did not have a “substantial factual basis” for his opinion that lead inside Spaulding

caused Christian’s elevated blood lead levels because he lacked “information concerning

other possible sources.” Levitas asks us to affirm this ruling. Relying on Ross v. Housing

                                            11
Authority of Baltimore City, 430 Md. 648 (2013), Levitas argues that Dr. Klein could not

conclude that Spaulding was a source of Christian’s lead exposure because he did not

consider other properties or conduct an independent investigation.15 We are not persuaded.

       Ross lends scant support to Levitas—markedly more facts underlie Dr. Klein’s

opinion than were present in that case. In Ross, lead testing was conducted on the subject

property, but the testing only detected lead-based paint on the exterior and one interior

surface. Ross, 430 Md. at 654–55. The testimony of the expert, Pamela Blackwell-White,

M.D., was quite equivocal—saying that if there was any lead-based paint in a property, she

assumed it was the most probable source of lead exposure “until proven otherwise,”

       15
          Levitas also relies heavily on City Homes, Inc. v. Hazelwood, 210 Md. App. 615
(2013). There, the plaintiff identified three properties as possible sources of lead exposure,
but he only provided his expert witness, Eric Sundel, M.D., with information on one of
them. Id. at 689. This information included Arc test results that found three lead-positive
exterior surfaces and 19 lead-positive interior surfaces. Id. at 624–25. Based upon these
results, Dr. Sundel opined that the property was a reasonably probable source of the
plaintiff’s lead exposure. Id. at 688. Because he relied on the report and ignored other
possible sources of lead exposure, the Court of Special Appeals concluded that Dr. Sundel
lacked a sufficient factual basis for his lead-source opinion. Id. at 687–89. But here, Dr.
Klein neither ignored the other identified possible source of Christian’s lead exposure nor
relied solely on the 2012 Arc Report. Indeed, one of the reasons he concluded that
Spaulding was a source of Christian’s lead exposure was that his FEP and blood lead levels
were first found to be elevated while he was living at Spaulding, even though his blood
lead levels were also elevated while he was living at Denmore. Additionally, we have
never held that an expert witness cannot rely on information obtained from other sources.
All that we require is an adequate supply of data and a reliable methodology for assessing
that data. Roy, 445 Md. at 42–43 (citation omitted); Exxon Mobil Corp. v. Ford, 433 Md.
426, 478, as supplemented on denial of reconsideration, 433 Md. 493 (2013) (citation
omitted). To the extent that Hazelwood is inconsistent with this proposition, we disagree
with that aspect of its analysis.

                                             12
especially if it was built before 1970.16 Id. at 660. Importantly, she testified that “she was

merely identifying ‘potential risk’ and could not make any statement as to causation with

certainty.” Id. at 664. We concluded that she lacked an adequate factual basis to opine

that the subject property was the source of the plaintiff’s lead exposure. Id. at 663. We

reasoned that because Dr. Blackwell-White could not explain how she weighed certain

pieces of information in reaching her conclusion, her opinion would confuse rather than

assist the trier of fact. Id.

       By contrast, Dr. Klein concluded—with a reasonable degree of medical certainty—

that Spaulding was a reasonably probable source of Christian’s lead exposure for several

reasons:

             The 2012 Arc Report found that 31 interior locations and five exterior
              locations tested positive for lead;

             Lead paint was banned federally in 1978, and therefore it was unlikely
              that Spaulding had been painted with lead-based paint since Christian
              lived there in the 1990s;

             DHCD records described the poor condition of the property;17

             An MDE certification indicated that Spaulding was not lead free;

       16
          Evidence also showed that the plaintiff in Ross v. Housing Authority of Baltimore
City, 430 Md. 648 (2013), could have been exposed to lead from several possible sources,
but the expert, Pamela Blackwell-White, M.D., concluded that the subject property was the
only source of the plaintiff’s lead exposure. Id. at 664. In this case, by contrast, Denmore
was the only other possible source identified—and the facts show that Dr. Klein considered
it when he reached his conclusion.
       17
           In Dr. Klein’s deposition testimony, he acknowledged that the Department of
Housing and Community Development (“DHCD”) records were from after Christian lived
at Spaulding. But given Betty’s and Nickolas’s testimony about the poor condition of
Spaulding while Christian lived there and the lack of evidence of repairs in the intervening
years, it was reasonable for Dr. Klein to consider these records.

                                             13
             Christian’s FEP and blood lead levels were first found to be elevated
              while he was living at Spaulding, when he had not yet lived
              anywhere else;

             Family members testified that Spaulding was in a deteriorated
              condition while Christian was living there and that Christian touched
              peeling paint at the property; and

             Christian regularly stayed at Spaulding during the day while his
              mother was at work, both when he lived there and when he lived at
              Denmore.

Dr. Klein acknowledged that Denmore was also a source of Christian’s lead exposure.

Thus, unlike the expert in Ross, he did not jump to the conclusion that Spaulding was a

source merely because it contained lead paint.18 Spaulding’s lead testing was one of

multiple facts that Dr. Klein considered when developing his lead-source opinion.

       The Dissent claims that expert witnesses in lead paint cases must exclude other

properties to opine that a particular property was a substantial contributing factor to the

       18
          Levitas makes two additional points. He asserts that the Arc Report is not direct
evidence of “lead paint hazards” while Christian lived at Spaulding, but merely evidence
of the presence of lead at the property in 2012. He contends that there must be
contemporaneous evidence of such hazards, like citations from the Baltimore Housing
Department, for Dr. Klein to have a sufficient factual basis to conclude that Spaulding was
a reasonably probable source of Christian’s lead exposure. We have never imposed such
a requirement. Rather, the adequacy of an expert’s factual basis turns on whether he had a
sufficient supply of data and a reliable methodology. Roy, 445 Md. at 42–43 (citation
omitted); Ford, 433 Md. at 478. As we explained, supra, Dr. Klein’s source causation
opinion satisfied these requirements.

        Levitas also claims that “Christian targeted [Spaulding], then provided Dr. Klein
with information pertaining only to that property.” Levitas mischaracterizes the record.
Dr. Klein’s own report lists the records that he reviewed in developing his opinion. On
that list is “[p]roperty information for 3605 Spaulding Avenue [and] 4946 Denmore
Avenue.”

                                            14
plaintiff’s injuries. Dissent Slip Op. at 22–23. It also contends that the plaintiff must

establish that “the subject property was a more probable source” of his injuries than other

possible sources.      Id. at 5.   Both of these assertions stem from a fundamental

misunderstanding of the substantial factor test. The substantial factor test applies when

“two or more independent negligent acts bring about an injury.” Pittway Corp. v. Collins,

409 Md. 218, 244 (2009). Under the test, an actor’s conduct is a cause-in-fact of the

plaintiff’s injuries when it is “a substantial factor in bringing about the harm.” Id. (quoting

Restatement (Second) of Torts § 431 (Am. Law Inst. 1965)). The substantial factor test

does not require experts to exclude other properties as possible contributing sources or the

plaintiff to show that one cause had a greater impact than any other substantial factor

causing the harm. See Eagle-Picher Indus., Inc. v. Balbos, 326 Md. 179, 209 (1992). It

would be illogical for us to require an expert to narrow the plaintiff’s lead exposure down

to a single source when the substantial factor test, by its very definition, permits more than

one cause of injury.

       The discretion accorded to trial judges in evidentiary rulings calls for an exercise of

judgment using applicable legal standards. Neustadter, 418 Md. at 241–42. Here, the trial

court excluded Dr. Klein’s proffered testimony about source causation because he had

“very little . . . information concerning other sources [of lead exposure].” In doing so, it

thus relied on a purported rule of law that an expert must exclude other properties before

he can testify that the plaintiff was exposed to lead at the subject property. But, as

discussed supra, this is not the rule. Moreover, in Hamilton v. Kirson, 439 Md. 501 (2014),

we dismissed concerns over the experts being “provided with little information on other

                                              15
potential sources of lead exposure.” Id. at 544. We explained, “[T]here may be other ways

that an injured plaintiff may establish that it was probable that the interior of a subject

house contained lead” besides eliminating other possible sources of lead exposure. Id. We

have only required that an expert be able to adequately explain how he determined that a

property was a source of the plaintiff’s lead exposure so that the trier of fact can evaluate

his reasoning. Ross, 430 Md. at 663–64 (citation omitted). By relying on the wrong legal

standard, the trial court abused its discretion.

                                      Medical Causation

         The first factor of Rule 5-702—qualification by knowledge, skill, experience,

training, or education—comes into play as we consider the Circuit Court’s exclusion of Dr.

Klein’s testimony about the cause of Christian’s injuries. Although the parties dispute the

exact grounds for this ruling, our examination of the record reveals that the Circuit Court

precluded Dr. Klein from testifying about Christian’s injuries both on the grounds that he

was not qualified and that he lacked an adequate factual basis. We assess both grounds

below.

         Levitas takes issue with the factual basis for Dr. Klein’s opinion that lead poisoning

caused “[m]ental [r]etardation” and “[i]mpaired cognition” in Christian. He argues that

Dr. Klein should have conducted his own examination of Christian, rather than relying on

Dr. Hurwitz’s report, scientific research, Christian’s school records, discovery materials,

and deposition testimony. This argument reflects Levitas’s misunderstanding about the

nature of—and boundaries for—expert testimony.

                                               16
       In a leading case on expert witness qualifications, Radman v. Harold, we held that

the trial court erred in precluding an internal medicine specialist from testifying about the

standard of care for a hysterectomy because he had not “performed any surgery of any

kind, let alone in the specialty of gynecology and urology.” 279 Md. at 174. There, we

explained, “[W]e perceive no reason why a person who has acquired sufficient knowledge

in an area should be disqualified as a medical expert merely because he is not a

specialist . . . .” Id. at 171 (emphasis in original).

       We recently reiterated in Roy the principle from Radman—that an expert witness is

“not required necessarily to be a specialist” or have “specialized knowledge,” but her

opinion must be based on “reliable knowledge, skill, and experience.” Roy, 445 Md. at 43,

50; see also Md. Rule 5-702(1). In Roy, the expert witness, Eric Sundel, M.D., a board-

certified pediatrician, had never studied or treated an individual with lead poisoning, but

was well-read on lead poisoning and its effects on children.19 Roy, 445 Md. at 33, 35. He

testified in his deposition that lead exposure at the subject property had caused the plaintiff

to suffer a loss of IQ points, impaired attention, and problems with memory and

coordination. Id. at 33. Although we acknowledged that Dr. Sundel “may not be the most

qualified expert witness on medical causation,” we nevertheless concluded that he was

competent to testify about medical causation, and the trial court abused its discretion in

excluding him. Id. at 43–44.

       19
         Dr. Sundel is the same expert the Court of Special Appeals held was properly
excluded in Hazelwood. The Roy Court distinguished the record in that case from the
record in Roy, noting that he had “endeavored to be more specific and shore-up the
supposed deficiencies in his qualifications.” Roy, 445 Md. at 50.

                                               17
       The record in this case establishes that Dr. Klein has the “knowledge, skill,

experience, training, or education” required under Rule 5-702(1). During his deposition,

Dr. Klein testified that he was an attending physician at the University of Maryland for 25

years, during which time he treated lead-poisoned children. Additionally, he testified that

he helps doctors in Israel, where he now practices, rule out lead poisoning as a cause of

illness. He is also well-acquainted with Centers for Disease Control and Prevention and

American Academy of Pediatrics literature on lead poisoning, and he has been testifying

as an expert witness in lead paint cases since 1995.

       The Circuit Court precluded Dr. Klein from testifying about Christian’s IQ loss on

the grounds that he did not administer the “particular type of IQ test” that Dr. Hurwitz used

in his own practice and he is “not able to explain to the jury how [ ] the psychologist got to

[his] results.” But physicians are often knowledgeable about many tests, even those they

do not use. Knowledge about a broad spectrum of available tests is part of the training

received by a physician—and this knowledge need not be acquired through hands-on

experience. Radman, 279 Md. at 170–71. In the lead paint litigation context, Roy makes

clear that an expert need not administer the IQ test to be competent to testify that lead

exposure caused a loss in IQ. In Roy, Dr. Hurwitz provided a neuropsychological report

on the plaintiff. The expert, Dr. Sundel, did not administer the IQ test. Instead, he relied

on Dr. Hurwitz’s report to conclude that the plaintiff suffered a loss of IQ points and other

attention and memory impairments. Roy, 445 Md. at 33. We nevertheless held that Dr.

Sundel was qualified to testify about the plaintiff’s injuries. Id. at 52.

                                              18
       Like Dr. Sundel, Dr. Klein developed his opinion based in part on Dr. Hurwitz’s

neuropsychological evaluation of Christian. Moreover, the record reflects that Dr. Klein

was indeed familiar with and had previously graded the IQ test. He testified in deposition

that he was “familiar enough with [the IQ test] to know how the test was generated,” had

seen several editions of different IQ tests, and “[knew] the testing pretty intimately.” In

short, Dr. Klein had ample knowledge, training, and experience to be qualified as an expert

under Rule 5-702(1). We see no sustainable reason why the trial court would conclude

otherwise.

       We next focus on whether Dr. Klein had a sufficient factual basis to testify as to

Christian’s IQ loss. Levitas submits that the court properly excluded Dr. Klein’s testimony

and takes issue with his reliance on Dr. Hurwitz’s neuropsychological report in developing

his medical causation opinion, without meeting Christian, his family, his teachers, or his

treating physicians. He also argues that Dr. Klein cannot calculate Christian’s IQ loss using

the Lanphear study because it is population-based, and therefore cannot be used to calculate

an individual’s IQ loss.

       As we have established, an expert can rely on facts and data “of a type reasonably

relied upon by experts in the particular field in forming opinions or inferences upon the

subject.” Md. Rule 5-703(a). An expert’s factual basis “may arise from a number of

sources, such as facts obtained from the expert’s first-hand knowledge, facts obtained from

the testimony of others, and facts related to an expert through the use of hypothetical

questions.” Sippio v. State, 350 Md. 633, 653 (1998); see also Rollins v. State, 161 Md.

App. 34, 86 (2005), aff’d, 392 Md. 455 (2006) (an autopsy report prepared by another

                                             19
doctor provided a sufficient factual basis for a medical expert to opine on the victim’s cause

of death). In Roy, this Court concluded that Dr. Sundel, who had also relied on a report

from Dr. Hurwitz, was competent to testify regarding the medical causation of the

plaintiff’s injuries. Roy, 445 Md. at 51. Here, Dr. Klein similarly relied on a report from

Dr. Hurwitz in developing his opinion on Christian’s lead-caused injuries. Based on our

conclusion in Roy, Dr. Klein’s reliance was proper—and the Circuit Court arbitrarily

exercised its discretion to exclude his testimony on that basis.

       In Roy, Dr. Sundel also used the Lanphear study to calculate the plaintiff’s

individual IQ loss. The Roy defendants argued that the study could not provide a sufficient

factual basis for Dr. Sundel’s IQ-loss opinion because other reputable studies contradicted

the Lanphear study’s results and cautioned against using it to calculate individual IQ loss.

Roy, 445 Md. at 51–52 n.16. We rejected this argument, explaining that “reliance on the

Lanphear study does not invalidate the entire basis of [an expert’s] opinion, even if the

Lanphear study is contrary to the results of other studies . . . . Such is the grist for cross-

examination and dueling experts and for resolution by the relative weight assigned by the

fact-finder.”20 Id. at 52. We reject Levitas’s argument for the same reasons.

       Finally, Levitas contends that Dr. Klein lacked a sufficient factual basis for his

opinion that Christian has “impaired cognition” due to: (1) a 10-point difference between

the IQ scores computed for Christian by Dr. Hurwitz and the defense expert; and (2) Dr.

       20
         We also acknowledged that the Lanphear study “has been cited to and discussed
extensively by other studies employing similar tests relating to IQ loss and childhood lead
poisoning.” Roy, 445 Md. at 51; see also id. at n.16 (listing some of the books and journals
that have cited the Lanphear study).

                                              20
Klein’s acknowledgment that there is no evidence of Christian being diagnosed with an

“attention impairment” or a learning disability.21 But these fact-based arguments go to the

weight of Dr. Klein’s testimony, not its admissibility. See Ford, 433 Md. 426 at 481

(rejecting the argument that an expert’s testimony was inadmissible because he did not

reach the same conclusions as the other party’s expert using the same data); Roy, 445 Md.

at 43 (“Cross-examination is the usual crucible for persuading the fact-finder which witness

merits the greater weight.”). As long as an expert’s opinion will assist the trier of fact in

understanding the evidence or determining a fact at issue, he should be permitted to testify.

See Md. Rule 5-702. Dr. Klein’s testimony would aid the jury in assessing the extent of

Christian’s alleged injuries because determining a person’s IQ and calculating potential IQ

loss are beyond the scope of the average juror’s realm of knowledge.

                                     CONCLUSION

       Because Dr. Klein is competent to testify about lead-source causation and medical

causation, the Circuit Court erred when it excluded his testimony. Therefore, we affirm

the judgment of the Court of Special Appeals.

                                          JUDGMENT OF THE COURT OF
                                          SPECIAL APPEALS AFFIRMED. COSTS
                                          TO BE PAID BY THE PETITIONER.

       21
          Levitas claims that “Dr. Klein conceded that the results of Dr. Hurwitz’s
evaluation of Christian were ‘suspect’” because Christian admitted to using marijuana and
alcohol daily. Therefore, Levitas contends, Dr. Hurwitz’s report could not provide an
adequate factual basis for Dr. Klein’s testimony. Levitas has taken Dr. Klein’s testimony
out of context. Speaking only to marijuana use, Dr. Klein testified that the “memory
function” portion of Dr. Hurwitz’s report “might be suspect.” This is grist for cross-
examination and does not affect admissibility.

                                             21
Circuit Court for Baltimore City
Case No.: 24-C-11-000954
Argued: February 6, 2017
                                   IN THE COURT OF APPEALS

                                          OF MARYLAND

                                                No. 58

                                        September Term, 2016

                                        STEWART LEVITAS

                                                  v.

                                   MICHAEL DAVON CHRISTIAN

                                         Barbera, C.J.
                                         Greene
                                         Adkins
                                         McDonald
                                         Watts
                                         Getty
                                         Battaglia, Lynne A. (Senior Judge,
                                          Specially Assigned),

                                                JJ.

                                    Dissenting Opinion by Getty, J.

                                         Filed: July 11, 2017
       I respectfully dissent from the Majority’s conclusion that Howard Klein, M.D., the

pediatrician expert witness offered by the Respondent, Michael Christian, offered a

sufficient factual basis for his opinion that lead-based paint inside the property owned by

Stewart Levitas, Petitioner, at 3605 Spaulding Avenue (“the Spaulding Property”), was a

substantial factor cause of Mr. Christian’s harm from lead poisoning. See Majority Slip

Op. at 11-16. Although I agree with the Majority that evidence in the record may have

been sufficient for Dr. Klein to reasonably conclude that Mr. Christian “was exposed to

lead-based paint at the [Spaulding Property],” Dr. Klein did not adequately explain the

methodology by which he reached that conclusion. And, the record does not show that Dr.

Klein had an adequate supply of data, or offered any methodology in support of his opinion

that it was Mr. Christian’s exposure to lead-based paint at the Spaulding Property that was

the substantial factor cause of his elevated blood lead levels and injuries from lead paint

poisoning, as opposed to his period of residency at another property at which he resided as

a child, 4946 Denmore Avenue (“the Denmore Property”), which Dr. Klein agreed also

appeared to be a source of lead ingested by Mr. Christian.

       Maryland courts have consistently held that an expert lacks an adequate factual basis

for an opinion as to source causation in a lead paint case unless the expert can show an

adequate supply of data and describe the methodology that enabled the expert to rule out

other reasonably probable sources of the plaintiff’s lead exposure and elevated blood lead

levels, and thereby show that it was the defendant’s property that was the substantial factor

cause of the plaintiff’s lead poisoning. As this Court held in its recent opinion in Roy v.
Dackman, “it is not enough for an expert to conclude that a certain property is the source

of the child’s exposure to lead when other probable sources have not been eliminated.”

445 Md. 23, 48 (2015). Indeed, we specifically held that expert opinion testimony as to

source causation that does not exclude other probable sources is “‘as likely to confuse as

to assist a jury.’” Id. (quoting Ross v. Hous. Auth. of Balt. City, 430 Md. 648, 664 (2013)).

       As Dr. Klein failed to provide a factual basis adequate to exclude the Denmore

Property as a probable source of Mr. Christian’s harm, as required by Roy, and did not

describe the methodology he used to reach his opinions as to lead source causation, I would

affirm the trial court’s grant of the motion to exclude his testimony regarding lead source

causation. Therefore, I respectfully dissent.

 A. Causation in Lead Paint Litigation

       When a plaintiff raises a negligence claim alleging injury from the presence of lead-

based paint in a property owned by a defendant, the plaintiff bears the burden of proof for

all essential elements of that claim, including “that the defendant’s negligence was a

proximate cause of the accident or injury.” Hamilton v. Kirson, 439 Md. 501, 526 (2014)

(quoting Peterson v. Underwood, 258 Md. 9, 15 (1970)). One aspect of proximate cause

is causation-in fact or, in other words, “whether [a] defendant’s conduct actually produced

an injury.” Id. When there are two or more independent possible causes of an injury,

courts apply the “substantial factor” test to determine whether a defendant’s conduct

produced the injury.

                                                 2
       This Court first applied the substantial factor test in a lead paint case in Ross v.

Housing Authority of Baltimore City, 430 Md. 648 (2013). In Ross, we explained that

substantial factor causation in a lead paint case “can be conceived as a series of links:”

              (1) the link between the defendant’s property and the plaintiff’s
              exposure to lead; (2) the link between specific exposure to lead
              and the elevated blood lead levels, and (3) the link between
              those blood lead levels and the injuries allegedly suffered by
              the plaintiff. To be a substantial factor in causing [a plaintiff’s]
              alleged injuries, the [subject property] must have been a source
              of [the plaintiff’s] exposure to lead, that exposure must have
              contributed to the elevated blood lead levels, and the associated
              increase in blood lead levels must have been substantial
              enough to contribute to her injuries.

Ross, 430 Md. at 668. The three links described in Ross can be labelled as “(1) source, (2)

source causation, and (3) medical causation.” Rogers v. Home Equity USA, Inc., No. 57,

Sept. Term 2016, Majority Slip Op. at 11. This Court later clarified that in order to

establish the first “source” link in the chain, “the plaintiff must tender facts admissible in

evidence that, if believed, establish two separate inferences: (1) that the property contained

lead-based paint, and (2) that the lead-based paint at the subject property was a substantial

contributor to the victim’s exposure to lead.” Kirson, 439 Md. at 529-30.

       A plaintiff may establish the required causation links in a lead paint case through

either direct or circumstantial evidence. Id. at 527. This Court has endorsed two separate

theories whereby a plaintiff may rely on circumstantial evidence to establish the first two

of the Ross links, “source” and “source causation.” Under a Dow theory, first articulated

by the Court of Special Appeals in Dow v. L & R Properties, Inc., a plaintiff may establish

that a property was the source of lead exposure, and that the exposure at that property

                                                   3
caused elevated blood lead levels, if the plaintiff can “rule out” other reasonably probable

sources of lead exposure, and thereby show that the subject property is the “only possible”

source of the plaintiff’s lead exposure. 144 Md. App. 67, 75-76 (2002). See also Kirson,

439 Md. at 530-37 (discussing Dow and cases applying a Dow theory of causation). And,

under a theory first articulated in a dicta hypothetical in Hamilton v. Kirson, 439 Md. at

537-38, and subsequently adopted in Rogers v. Home Equity USA, Inc., this Court has held

that at the summary judgment stage of litigation, even without excluding other reasonable

probable sources of lead, a plaintiff may “rule in” a defendant’s property as a source of

lead exposure by showing a “reasonable probability” that the property contributed to the

lead exposure, and that the exposure was a “reasonably probable source” of the plaintiff’s

elevated blood lead levels. No. 57, Sept. Term 2016, Majority Slip Op. at 13, 21.

       I dissented from this Court’s endorsement and application of a new theory of

causation in Rogers. In part, that dissent was based on my view that, the proper standard

of proof under which a plaintiff’s case should be scrutinized at the summary judgment

stage is whether the plaintiff has shown that it was “more probable than not” that a

particular property was a substantial factor cause of his exposure to lead and elevated blood

lead levels, as opposed to a “reasonable probability.”1 Rogers, Dissenting Slip Op. at 10-

15. But, of greater significance to the motion to exclude at issue in this case, I also

       1
         In the context of lead paint litigation, the Court first distinguished a “reasonable
probability,” which it equated to a “fair likelihood,” from a more stringent “more probable
than not” standard in Rowhouses, Inc. v. Smith, 446 Md. 611 (2016). In that case, the Court
explained that “a reasonable probability is less than more likely than not, but more than a
possibility.” Id. at 659.
                                                 4
disagreed with the Rogers Majority’s narrow focus on evidence as to the subject property

owned by the defendant, when other evidence in the record indicated that another property

was an equally likely source of the plaintiff’s harm. Id. at 15-19. In my view, when there

are multiple potential sources of a plaintiff’s exposure to lead-based paint and elevated

blood lead levels, each of which is more than a mere possible source of the harm, and the

plaintiff has claimed that only one of them was the source of his harm, the plaintiff must,

at a minimum, show that the subject property was a more probable source of that exposure

and elevated blood lead levels than the other potential source(s) in order to establish that

the subject property was a substantial factor cause of his harm. Id. See also Peterson v.

Underwood, 258 Md. 9, 17 (1970) (holding that “where plaintiff by his own evidence

shows two or more equally likely causes of the injury, for only one of which defendant is

responsible, plaintiff can not recover”).

       The Majority in this case asserts that the standard which I described in my dissent

in Rogers “stem[s] from a fundamental misunderstanding of the substantial factor test.”

See Majority Slip Op. at 14-15. The Majority notes that the substantial factor test “applies

when ‘two or more independent negligent acts bring about an injury.’” Id. (quoting Pittway

Corp. v. Collins, 409 Md. 218, 244 (2009)). As “the substantial factor test, by its very

definition, permits more than one cause of injury,” the Majority concludes that “[i]t would

be illogical for us to require an expert to narrow the plaintiff’s lead exposure down to a

single source.” Id.

       A plaintiff may certainly raise a claim under the substantial factor test that there was

more than one cause of his harm. As I noted in a footnote in my Rogers dissent, in a lead

                                                  5
paint negligence case a plaintiff may claim “that the defendant’s property is a contributing

source of his harm from lead exposure, as part of a claim that multiple sources of lead

exposure cumulatively proximately caused his harm.” Rogers, Dissenting Slip Op. at 5

n.1. (Emphasis in original). In such a scenario, I believe that the appropriate burden that

the plaintiff would need to meet would be to show that the causes that he identified,

considered as a whole, were a more probable than not source of his harm. But, firstly, the

plaintiff must actually raise such a claim, and produce evidence in support of it as to the

other alleged sources of lead exposure. And, secondly, as the Court of Special Appeals

pointedly noted in Hamilton v. Dackman, such a claim would be a “hard case” to establish,

because “a plaintiff would need to produce probability-level evidence as to exposure at

each property separately.” 213 Md. App. 589, 616 (2013).

       In contrast, when a plaintiff only identifies a single property that he claims was the

source of his exposure to lead and lead poisoning, but evidence before the trial court shows

that there are other reasonably likely sources of that harm, the question before the trier of

fact is not whether the defendant’s property was merely a contributor to some of his lead

exposure along with the other cause(s) the plaintiff has identified. Rather, the issue

becomes whether that property was, compared to the other reasonably likely causes, a

substantial contributor to the plaintiff’s lead exposure and consequent lead poisoning. In

such a case, although the plaintiff does not need to show that a defendant’s property was

the only contributing cause of his lead exposure and injury, he must show at least that the

property was “an important or significant contributor to [his] injuries.” Rogers, No. 57,

Sept. Term 2016, Dissenting Slip Op. at 7 (quoting Black’s Law Dictionary (10th ed.

                                                 6
2014)). In my view, that requires the plaintiff to show that the defendant’s property was a

more probable source of his exposure and elevated blood lead levels than the other

property(s).

       Expert Testimony and Causation

       Under either a Dow or Kirson/Rogers theory of causation, a plaintiff can overcome

summary judgment and place the issue of whether the defendant’s property caused the

plaintiff’s lead exposure and elevated blood lead levels before the trier of fact through a

sufficient showing of direct or circumstantial evidence. Dow, 144 Md. App. at 75; Rogers,

Majority Slip Op. at 13. The plaintiff is not required, as a matter of law, to have an expert

opinion as to causation. See e.g., Ross, 430 Md. at 669 (holding that “the link between a

defendant’s property and a plaintiff’s childhood exposure to lead paint and dust may be

established through circumstantial evidence, even if expert opinion testimony is not

available”). However, expert opinion may be necessary in some instances for a plaintiff to

overcome summary judgment, depending on the nature and extent of the evidence. See

e.g., Rogers, Majority Slip Op. at 25-26 (overturning trial court’s grant of summary

judgment based in part upon expert testimony as to the effect of continuing exposure to

lead on the plaintiff’s blood lead levels, from which “a jury could reasonably infer that if

[defendant’s property] was not contributing source [of lead exposure,]” plaintiff’s blood

lead levels would have decreased while living at that property). And, of course, a plaintiff

who overcomes summary judgment still bears the burden of proof as to the element of

causation at trial, where expert opinion can play a critical role in persuading a jury.

                                                  7
       The standard for admissibility of expert testimony as to source causation is thus a

vital one in lead paint actions. The Majority holds today that an expert who gives an

opinion that a defendant’s property caused a plaintiff’s harm does not need to show or

explain that other reasonably probable sources did not cause the plaintiff’s harm. Majority

Slip Op. at 15 (holding that it is “not the rule” that a source causation expert in a lead paint

action “must exclude other properties before he can testify that the plaintiff was exposed

to lead at the subject property”) The Majority’s removal of the requirement that a source

causation expert must exclude other reasonably probable sources in order for his expert

testimony to be admitted at trial, in combination with the Court’s earlier decision in Rogers,

is likely to lead to the widespread adoption of the new Kirson/Rogers theory of causation

in lead paint actions, and the abandonment of the Dow theory. When a plaintiff has resided

at more than one property that may have contained lead paint, he is unlikely to go to the

time and expense of gathering evidence or obtaining an expert opinion to exclude all the

properties that did not cause his harm if, instead, he can simply focus in on a particular

defendant’s property and show that it was a reasonably probable source of its harm.

However, as I shall explain below, the Majority’s holding is not only likely to usher in a

major change in the conduct of lead paint negligence actions but, more importantly, is also

inconsistent with the factual basis requirement in Maryland Rule 5-702 and Maryland

precedent interpreting that requirement in lead paint actions.

                                                   8
       B. Factual Basis Requirement for Expert Opinion Testimony in Lead Paint
       Litigation

       Maryland Rule 5-702 states that “[e]xpert testimony may be admitted, in the form

of an opinion or otherwise, if the court determines that the testimony will assist the trier of

fact to understand the evidence or to determine a fact in issue.” A trial court “bases this

determination on three factors,” one of which is “‘whether a sufficient factual basis exists

to support the expert testimony.’” Id.

       Maryland Rule 5-702’s requirement of an adequate factual basis is necessary to

ensure that an expert’s testimony “constitutes more than mere speculation or conjecture.”

Roy, 445 Md. at 42 (quoting Exxon Mobil Corp. v. Ford, 433 Md. 426, 478, as

supplemented on denial of reconsideration, 433 Md. 493 (2013)). That factual basis “may

arise from a number of sources, such as facts obtained from the expert’s first-hand

knowledge, facts obtained from the testimony of others, and facts related to an expert

through the use of hypothetical questions.” Id. at 43 (quoting Taylor v. Fishkind, 207 Md.

App. 121, 143 (2012), cert. denied, 431 Md. 221 (2013)). In order to assess the adequacy

of the factual basis, a trial court looks at two factors: first, that the expert “[has] available

an adequate supply of data with which to work,” and second, that the expert “employ[s] a

reliable methodology in analyzing that data.” Id. at 42-43 (quoting CSX Transp., Inc. v.

Miller, 159 Md. App. 123, 189 (2004).

       Maryland appellate courts have had several occasions in recent years to apply these

principles in lead paint litigation to evaluate the adequacy of the factual basis supporting

an expert opinion offered by a pediatrician as to source or source causation—that a

                                                   9
plaintiff’s elevated blood lead levels and harm from lead poisoning were caused by

exposure to lead while living at the subject property owned by the defendant.

              Court of Special Appeals Cases

       In Taylor v. Fishkind, the Court of Special Appeals considered whether a trial court

had abused its discretion in granting summary judgment in favor of the defendant based

upon a finding that the plaintiff’s pediatrician expert witness, Dr. Henri Merrick, lacked an

adequate factual basis as to his opinions regarding lead paint source and source causation.

207 Md. App. 121, 124 (2012), cert. denied, 431 Md. 221 (2013). Dr. Merrick’s report

concluded that the plaintiff was exposed to lead-based paint at two separate properties,

based on “the age of the dwellings, the described conditions of the first dwelling, the

detection of lead in an exterior window apron of this first dwelling and [the plaintiff’s]

blood lead levels while living at each dwelling.” Id. at 130.

       The Court of Special Appeals determined that Dr. Merrick’s opinion that the

property contained lead-based paint was “only supported by the age of the house and the

presence of lead on one component of the exterior of the house.” Id. at 142. The

intermediate appellate court explained that he could not rely upon a presumption that the

house contained lead paint simply “because it was built at a time when many houses

contained lead-based paint.” Id. Moreover, the court discounted the exterior testing

because the plaintiff had provided only “scant” circumstantial evidence that the interior of

the property contained lead-based paint. Id. at 142. Likewise, the Court of Special Appeals

concluded that the only evidence on which the expert relied to conclude that the plaintiff

was exposed to lead at the defendant’s property was evidence that her blood lead levels

                                                10
were elevated while she resided there. Id. at 145. The Court of Special Appeals held that

“more is required to support Dr. Merrick’s opinion that [the plaintiff] was exposed to lead-

based paint at [the defendant’s property]” because she conceded that she could not prove

that elevated level was caused by the plaintiff’s move to that property, as opposed to other

properties where she had resided. Id. This Court subsequently denied the plaintiff’s

petition for a writ of certiorari. 431 Md. 221 (2013).

       The Court of Special Appeals considered a factually similar case in City Homes,

Inc. v. Hazelwood, in which the plaintiff’s pediatrician expert, Dr. Eric Sundel, testified

that the property owned by the defendant “was the source of the [plaintiff’s] lead exposure”

and “a substantial contributing factor to injuries [the plaintiff] sustained.” 210 Md. App.

615, 687, cert. denied, 432 Md. 468 (2013). The intermediate appellate court held that Dr.

Sundel’s testimony lacked a sufficient factual basis, and the circuit court abused its

discretion in permitting that testimony, because Dr. Sundel had “limited knowledge of [the

plaintiff’s] . . . potential exposure to lead from other sources,” and had “failed to investigate

other potential sources—i.e., to determine whether lead had been found in other residences

in which appellee had lived or visited—to gain insight into whether [the defendant’s

property] was a source of [the plaintiff’s] lead exposure.” Id. at 689. This Court declined

to grant the plaintiff’s petition for a writ of certiorari. 432 Md. 468 (2013).

              Court of Appeals Cases

       In Ross v. Housing Authority of Baltimore City, this Court first addressed whether a

pediatrician’s proposed expert opinion testimony that a defendant’s building was the source

of the plaintiff’s exposure to lead and harm from lead poisoning was supported by an

                                                  11
adequate factual basis. 430 Md. 648 (2013). In that case, the plaintiff had resided at several

homes as a child, and had elevated blood lead levels while she was living at the property

owned by the defendant and at another property. Id. at 651-54. Lead testing on the

defendant’s property detected lead-based paint on the exterior and one interior surface. Id.

at 654-55. The plaintiff’s expert, Dr. Jacalyn Blackwell-White, had reviewed “various

records concerning [the plaintiff] and her two residences,” and, based on that review, had

“opined that Ms. Ross had been exposed to lead-based paint at both residences, that such

exposure ‘resulted in sustained toxic blood levels’ during her early developmental years.”

Id. at 656. However, Dr. Blackwell-White also gave an opinion that the defendant’s

property was “the source” of the plaintiff’s elevated blood lead levels for a two year period.

Id. at 659. She explained that “[i]f there is lead-based paint inside a house, [she would]

consider it to be a contributing cause to elevated lead levels,” and that “she would assume

the home to be the most probable source of elevated blood lead levels ‘until proven

otherwise,’ particularly if the house was built before 1970.” Id. at 660.

       This Court affirmed the circuit court’s grant of a motion to exclude Dr. Blackwell-

White’s testimony as lacking an adequate factual basis. Id. at 662-63. We concluded that

“Dr. Blackwell–White did not explain adequately how she reached the conclusion that the

[defendant’s] home was ‘the source’ of the lead exposure that resulted in [the plaintiff’s]

elevated blood lead levels.” Id. at 663. We emphasized that “[m]erely reciting certain

information that she took into account and then stating the ultimate conclusion without

explaining how and by what expert method that information was weighed did not provide

a basis by which the trier of fact could evaluate that opinion.” Id.

                                                 12
       Furthermore, we noted that because there was evidence in the record as to “various

other sources of lead exposure in [the plaintiff’s] environment,” there were multiple

potential causes of the plaintiff’s exposure and elevated blood lead levels, and thus “[t]he

real question for the fact-finder is how much exposure to lead at the [defendant’s property]

contributed to [the plaintiff’s] [elevated] blood lead levels over the pertinent time period.”

Id. at 664. As Dr. Blackwell-White did not offer any definitive opinion as to that question,

we held that her “ultimate conclusion identifying the [defendant’s property] as ‘the source’

was as likely to confuse as to assist a jury.” Id. We concluded our analysis by cautioning

that permitting an expert to testify under such circumstances could improperly give the

expert’s opinion “the imprimatur of court-endorsed expert status,” leading to a “risk that a

jury would give the opinion undue weight because it was stated by a court-qualified

expert.” Id.2

       Prior to today’s opinion, this Court most recently addressed whether there was an

adequate factual basis for a pediatrician expert’s opinion as to source and source causation

       2
        After Ross was published, the Court of Special Appeals in Hamilton v. Dackman,
213 Md. App. 589, 591-92 (2013) upheld a circuit court’s grant of summary judgment in a
lead paint case, a ruling which the circuit court based in part upon its rejection of the
testimony of Dr. Blackwell-White, as well as other experts. The Court of Special Appeals,
applying Ross, concluded that Dr. Blackwell-White lacked a sufficient factual basis for her
opinion. Id. at 614. The intermediate appellate court noted that, just as in Ross, Dr.
Blackwell-White had improperly relied on an assumption that lead paint was present in the
house based upon its age. Id. Moreover, the Court of Special Appeals determined that she
had once again “reached a conclusion as to the source [of the plaintiff’s lead poisoning]
notwithstanding the presence of other potential sources of lead, and as such her opinion
‘was as likely to confuse as to assist a jury.’” Id. (quoting Ross, 430 Md. at 664). This
Court subsequently quoted the Court of Special Appeals’ reasoning as to the lack of an
adequate factual basis in Hamilton v. Dackman approvingly in our opinion in Kirson, 439
Md. at 538-42.
                                                 13
in a lead paint case in Roy v. Dackman, 445 Md. 23 (2015). In Roy, the petitioner, through

his mother, filed a suit against the respondent property owners, alleging that the owners’

property was “the only source of lead paint” which he had ingested as a child. Id. at 30.

The petitioner had resided for the first eight months of his life at another property before

moving to that owned by the respondents, where he then resided for a two year period. Id.

at 31. During his period of residency at the respondents’ property, tests were performed

that showed elevated blood lead levels. Id. at 32. The respondent’s property was built in

1920, and petitioner’s counsel had obtained testing of the exterior of the property positive

for lead-based paint. Id. at 31-32. Petitioner’s mother also testified to the presence of

flaking and chipping paint in both the interior and exterior of the property. Id. Based on

those facts, the petitioner’s expert pediatrician, Dr. Eric Sundel (also an expert in the Court

of Special Appeals’ holding in Hazelwood, supra), indicated that he would give an opinion

that lead-based paint at the property caused the petitioner’s injuries. Id. at 33. The

respondents thereafter moved to exclude Dr. Sundel’s testimony, and the circuit court

granted the motion. Id. at 36-37.

       This Court held that the circuit court did not abuse its discretion in excluding Dr.

Sundel’s testimony, concluding that there was not an adequate factual basis, and the

“proposed opinion falls victim to the same problems as those discussed in Taylor and

Ross.” Id. at 47. We determined that the proposed opinion “was based solely on scant

circumstantial evidence, including the age of the home and exterior tests of the paint on the

dwelling,” and “did not rule out other probable sources” of lead exposure. Id. at 47-48.

                                                 14
Furthermore, we noted that there was “no discussion in the record of Dr. Sundel’s methods”

that he used to reach his opinion. Id. at 48.

       Notably in Roy, we referenced our opinion in Kirson, 439 Md. at 537-38, where we

had indicated in dicta that a plaintiff may be able to show sufficient evidence to “rule in”

a property as containing lead-based paint even without excluding all other possible

sources.3 Nevertheless, we held in Roy that, without excluding other potential sources of

lead, there is not an adequate factual basis “for an expert to conclude that a certain property

is the source of [a] child’s exposure to lead when other probable sources have not been

eliminated.” Roy, 445 Md. at 47. (Emphasis added). Roy thus expressly recognized a

distinction in the law that, in my view, is critical to this appeal. On the one hand, a plaintiff

may be able to make a sufficient evidentiary showing to “rule in” a subject property as a

probable source of his lead poisoning without needing to put forth evidence to exclude

other probable sources of the plaintiff’s lead exposure. But, on the other hand, an expert

opinion that identifies a particular property as the source of the plaintiff’s lead poisoning

       3
         Roy specifically refers to our “holding” in Kirson that “a lead poisoning case may
succeed grounded on suitable circumstantial evidence as to source.” Id. However, the
Kirson Court only supplied a dicta hypothetical to illustrate that a plaintiff may be able to
establish circumstantially that a property contained lead-based paint. See Rogers, No. 57,
Sept. Term, Dissent Slip Op. at 6-8. Subsequently, after Roy was issued, this Court held
in Rogers v. Home Equity USA, Inc. that a plaintiff can “rule in” a property as a source of
lead exposure by showing that there is a “reasonable probability” that the plaintiff was
exposed to lead paint at that property, and that the exposure was a “reasonably probable
source” of his elevated blood lead levels. No. 57, Sept. Term 2016, Majority Slip Op. at
13, 21.

                                                  15
requires an adequate factual basis that includes evidence sufficient for the expert to exclude

other probable sources.

       The Roy Court appeared to rest this distinction upon Rule 5-702’s statement that

“[e]xpert testimony may be admitted . . . if the court determines that the testimony will

assist the trier of fact to understand the evidence or to determine a fact in issue.” As the

Court explained, when there are multiple reasonably probable sources of the plaintiff’s lead

exposure, an expert opinion that does not explain why it was the defendant’s property that

was a substantial factor that caused the plaintiff’s harm, as opposed to another property, is

“as likely to confuse as to assist a jury.” Id. at 48 (quoting Ross, 430 Md. at 664).

              Factual Basis Standard for Causation Expert Opinions Offered In a Lead
              Paint Negligence Action

       I distill from reviewing the above-described cases4 that an expert opinion in a lead

paint case as to source and source causation—that a plaintiff’s elevated blood lead levels

were caused by exposure to lead while living at the subject property owned by the

defendant—is supported by an adequate factual basis pursuant to Maryland Rule 5-702

only when three conditions are met. First, the data on which the expert relies to form his

opinion must be more than “scant” circumstantial evidence. Roy, 445 Md. at 47; Taylor,

207 Md. App. at 142. See also Hamilton v. Dackman, 213 Md. App. at 608 (noting that

       4
         In addition to the cases described above, the Court of Special Appeals has held in
Rochkind v. Stevenson that a trial court did not abuse its discretion by permitting a
pediatrician expert to testify as to source causation in a lead paint case. 229 Md. App. 422,
cert. granted, 450 Md. 663 (2016). Rochkind was thereafter accepted for certiorari to this
Court and, as of the date of this dissent, has not yet been decided. As this Court has not
yet determined if Rochkind was correctly decided, I did not rely upon it in this dissent.
                                                 16
“an expert cannot transform thin evidence or assumptions into viable causal connections

simply by labeling them an expert opinion”). Second, when a plaintiff has resided in at

least one property other than that owned by the defendant, which evidence shows was a

reasonably likely source of lead-based paint, the expert must be provided with, and show

to the trial court, data adequate for him to rule out the other property(s) as probable sources

of the plaintiff’s lead exposure and elevated blood lead levels. Roy, 445 Md. at 47; Ross,

430 Md. at 664; Hazelwood, 210 Md. App. at 689; Taylor, 207 Md. App. at 145. Third,

the expert must explain the methodology he used to reach his conclusions regarding source

and source causation so that the trier of fact can evaluate that methodology, as opposed to

merely reciting the facts on which he relied and then state his ultimate conclusions. Roy,

445 Md. at 48; Ross, 430 Md. at 663.

       C. Factual Basis in this Case

       I agree with several portions of the Majority’s analysis with respect to the factual

basis for Dr. Klein’s testimony as to source causation. Initially, I agree with the Majority

that Dr. Klein did not lack an adequate factual basis for his opinion merely because he did

not conduct an “independent investigation” or otherwise obtain first-hand knowledge of

Mr. Christian or the properties at issue. It is true that Dr. Klein was not a treating physician,

and that he had not seen or questioned Mr. Christian or his family members directly. He

stated in his deposition testimony that all of his opinions in the report that he prepared for

trial were based upon records that he had received from Mr. Christian’s counsel’s office.

Additionally, Dr. Klein offered opinions in response to several hypothetical questions

during that deposition. However, as the Majority notes, “we have never held that an expert

                                                  17
witness cannot rely on information obtained from other sources.” Majority Slip Op. at 12

n.15. Indeed, we have explicitly held that an expert’s factual basis “may arise from a

number of sources,” including “facts obtained from the testimony of others, and facts

related to an expert through the use of hypothetical questions.” Roy, 445 Md. at 43 (quoting

Taylor v. Fishkind, 207 Md. App. 121, 143 (2012)).

       Furthermore, I agree with the Majority that Dr. Klein had adequate data to support

his expert opinion that, to reasonable degree of medical probability, Mr. Christian “was

exposed to lead-based paint at the [Spaulding Property].” As the Majority notes, there was

substantial circumstantial evidence on which Dr. Klein relied in formulating that opinion:

       Dr. Klein concluded—with a reasonable degree of medical certainty—that
       Spaulding was a reasonably probable source of Christian’s lead exposure for
       several reasons:

           The 2012 Arc Report found that 31 interior locations and five exterior
            locations tested positive for lead;

           Lead paint was banned federally in 1978, and therefore it was unlikely
            that Spaulding had been painted with lead-based paint since Christian
            lived there in the 1990s;

           [Department of Housing and Community Development] records
            described the poor condition of the property;

           A[ ] [Maryland Department of the Environment] certification
            indicated that Spaulding was not lead free;

           Christian’s [free erythrocyte protoporphyrin (“FEP”)] and blood lead
            levels were first found to be elevated while he was living at
            Spaulding, when he had not yet lived anywhere else;

           Family members testified that Spaulding was in a deteriorated
            condition while Christian was living there and that Christian touched
            peeling paint at the property; and

                                                18
            Christian regularly stayed at Spaulding during the day while his
             mother was at work, both when he lived there and when he lived at
             Denmore.

Majority Slip Op. at 13-14.5 (Emphasis in original, footnote omitted). The 2012 Arc

Report that determined multiple interior locations of the Spaulding Property tested positive

for lead was not direct evidence that lead-based paint was present during the period of time

that Mr. Christian resided at that property. But, when combined with the fact that lead

paint had been banned federally prior to Mr. Christian’s period of residency at the

Spaulding Property, it was strong circumstantial evidence that lead paint was present on

the property during the relevant time period. Moreover, the evidence of Mr. Christian’s

elevated lead blood tests at the Spaulding Property, the Department of Housing and

Community Development records describing the poor condition of the property, as well as

interrogatory testimony of several of Mr. Christian’s relatives that described poor condition

of the property while Mr. Christian lived there and that he regularly stayed in the home

during the daytime, while circumstantial, was more than “scant” evidence that Mr.

Christian was exposed to lead while living at that property. Dr. Klein thus had sufficient

data from which he could conclude that defects in the Spaulding Property’s interior such

as chipping and flaking paint exposed Mr. Christian to lead while residing at that property.

       5
         The Majority is also correct in noting that Dr. Klein, unlike several of the experts
in the cases discussed above, did not make the mistake of concluding solely or primarily
from the age of the property that it must have contained lead paint, to which the plaintiff
was exposed. See e.g. Taylor, 207 Md. App. at 142. Although Dr. Klein considered the
age of the Spaulding Property, it was just one of several factors upon which he relied to
formulate his opinion that Mr. Christian was exposed to lead at that property.
                                                19
       However, Dr. Klein did not explain the methodology he used to assess that data and

reach his conclusion that Mr. Christian was exposed to lead at the Spaulding Property.

Instead, in both his report and his deposition testimony, he merely cited the “information

that [he] took into account and then stat[ed] [his] ultimate conclusion without explaining

how and by what expert method that information was weighed.” Ross, 430 Md. at 663. As

this Court held in Ross, that kind of recitation by an expert of the information relied upon,

without any explanation, “did not provide a basis by which the trier of fact could evaluate

th[e] opinion.” Id. As Dr. Klein did not detail his methodology in support of his opinion

that Mr. Christian was exposed to lead at the Spaulding Property, I cannot agree that he

had a sufficient factual basis for that opinion.

       Much more troubling, however, is that the Majority has overlooked the absence of

any factual basis or methodology in support of Dr. Klein’s additional opinion that it was

Mr. Christian’s exposure to lead-based paint at the Spaulding Property that was the

substantial factor cause of his elevated blood lead levels and injuries from lead poisoning,

as opposed to his period of residency at the Denmore Property, which Dr. Klein agreed was

also a source of his exposure to lead. The Majority states that Dr. Klein did “not

ignore[ ]” and “considered” information in the record as to the Denmore Property,

referencing his report in which he stated that he considered “[p]roperty information for

3605 Spaulding Avenue [and] 4946 Denmore Avenue.” Majority Slip Op. at 12 n.15, 14.

However, it was not sufficient for Dr. Klein to have merely looked at or briefly

“considered” information as to the Denmore Property. Rather, under this Court’s precedent

in Ross and Roy, he needed to put forth an adequate supply of data to show that it was

                                                   20
exposure to lead at the Spaulding Property, and not the Denmore Property, that was the

probable substantial cause of his harm from lead poisoning. See Roy, 445 Md. at 47; Ross,

430 Md. at 663-64. And, he needed to explain what methodology he used to rule out the

Denmore Property as a probable source of exposure. Id.

       Based on the evidence in the record, Dr. Klein both failed to offer an adequate

supply of data and failed to describe his methodology in support of his opinion that the

Spaulding Property was the substantial factor cause of Mr. Christian’s elevated blood lead

levels and harm from lead poisoning. Some of the data on which Dr. Klein relied indicated

a possibility that the Spaulding Property was a substantial factor cause of his elevated blood

lead levels. Specifically, Mr. Christian had an elevated blood lead level of 9 [μ]g/dL on

February 20, 1992, when he was just over two years old, and, according to the testimony

of his relatives, at that time, he had not “yet lived anywhere else.” See Majority Slip Op.

at 2, 14. However, there was also evidence that after Mr. Christian subsequently moved to

reside at the Denmore Property in October 1992, his blood lead levels significantly

increased while he resided at that property, first to 10 μg/dL in February 18, 1993 and then

to 17 μg/dL on July 16, 1993. Id. at 2. The record thus indicates that Mr. Christian’s blood

lead levels rose both while he was residing at the Spaulding Property, and while he resided

at the Denmore Property. But, Dr. Klein never identified the data on which he relied to

conclude that it was the initial exposure at the Spaulding Property, and not what appears to

be a subsequent exposure at the Denmore Property, that was the substantial cause of his

harm from lead poisoning. Nor did he describe any methodology that he had used to reach

that conclusion.

                                                 21
       Relying on the Court’s suggestion in Kirson, 439 Md. at 537-38, 544, that a plaintiff

may be able to show that a property was a source of lead exposure without excluding other

reasonably probable sources of such exposure, the Majority holds that it “is not the rule”

in Maryland that an expert as to source causation in a lead paint case must “exclude other

[reasonably probable] properties before he can testify that the plaintiff was exposed to lead

at the subject property.” Majority Slip Op. at 15. The Majority is incorrect. As noted

above, when this Court last considered expert testimony as to lead paint source causation

in Roy, the Court recognized that Kirson had suggested “that a lead poisoning case may

succeed grounded on suitable circumstantial evidence as to source,” without needing to

exclude other properties. Roy, 445 Md. at 47. Nonetheless, the Court expressly held in

Roy that expert testimony must be held to a higher standard, holding that “it is not enough

for an expert to conclude that a certain property is the source of [a] child’s exposure to lead

when other probable sources have not been eliminated.” Id.

       The Majority today is, therefore, overturning an express holding of this Court, less

than two years from the date that holding was issued, in direct contravention of the principle

of stare decisis. See e.g., DRD Pool Serv., Inc. v. Freed, 416 Md. 46, 63 (2010) (describing

stare decisis as meaning “to stand by the thing decided,” and that it is “the preferred course

because it promotes the evenhanded, predictable, and consistent development of legal

principles, fosters reliance on judicial decisions, and contributes to the actual and perceived

integrity of the judicial process”). The holding in Roy from which the Majority departs

today was not an outlier but rather, as I described above, entirely in accord with this Court’s

precedent in Ross, as well as the Court of Special Appeals’ holdings in Taylor and

                                                 22
Hazelwood. Moreover, in Roy and Ross this Court provided a cogent reason for requiring

a lead source expert to exclude other probable sources—explaining that permitting an

expert to opine that the defendant’s property was the substantial cause of the plaintiff’s

lead poisoning, without explaining why other properties that evidence in the record showed

were reasonably probable causes of exposure were not, is “as likely to confuse as to assist

a jury.” Roy, 445 Md. at 48 (quoting Ross, 430 Md. at 664). However, the Majority has

offered no such rationale for its holding today that sweeps away that requirement.

       D. Conclusion

       In summary, I would hold that when an expert witness is offered to show that a

plaintiff was exposed to lead at a particular property, and that the exposure at that property

caused the plaintiff’s elevated blood levels and injury from lead poisoning, that expert

meets the requirement in Maryland Rule 5-702 to show adequate factual basis only when

he relies on more than “scant” circumstantial evidence, rules out other reasonably probable

sources of the plaintiff’s lead exposure and elevated blood lead levels, and explains the

methodology he used to reach his conclusions. As to Dr. Klein’s first opinion that Mr.

Christian was exposed to lead-based paint at the Spaulding Property, while I agree there

was adequate data in the record to support that opinion, Dr. Klein failed to explain the

methodology he used to reach the opinion so that a trier-of-fact could properly assess it.

And, as to his second opinion that Mr. Christian’s exposure at the Spaulding Property was

a substantial factor cause of his harm, Dr. Klein did not identify any data or methodology

to show that the Spaulding Property was a more probable source of the harm than the

Denmore Property.

                                                 23
       The Majority’s holding that Dr. Klein was not required to exclude other probable

sources of Mr. Christian’s lead poisoning is contrary to this Court’s prior holdings in Ross

and Roy. Furthermore, the Majority’s holding will encourage trial courts to place the

“imprimatur of court-endorsed expert status” on expert opinions that do not clearly

establish that the defendant’s property was, more likely than not, a substantial factor cause

of the plaintiff’s harm, and thereby lead to confusion among jurors who are called to decide

that very issue. See Ross, 430 Md. at 664.

       For the above stated reasons, I would affirm the trial court’s grant of the motion to

exclude Dr. Klein’s testimony regarding lead-source causation and, therefore, I respectfully

dissent.

                                                24