(Slip Opinion) OCTOBER TERM, 2012 1 

Syllabus 

NOTE: Where it is feasible, a syllabus (headnote) will be released, as is

being done in connection with this case, at the time the opinion is issued.

The syllabus constitutes no part of the opinion of the Court but has been

prepared by the Reporter of Decisions for the convenience of the reader. 

See United States v. Detroit Timber & Lumber Co., 200 U. S. 321, 337. 

SUPREME COURT OF THE UNITED STATES 

Syllabus 

COMCAST CORP. ET AL. v. BEHREND ET AL. 

CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR 

THE THIRD CIRCUIT 

No. 11–864. Argued November 5, 2012—Decided March 27, 2013 

Petitioners, Comcast Corporation and its subsidiaries, allegedly “cluster” their cable television operations within a particular region by

swapping their systems outside the region for competitor systems inside the region. Respondents, named plaintiffs in this class-action

antitrust suit, claim that they and other Comcast subscribers in the 

Philadelphia “cluster” are harmed because Comcast’s strategy lessens

competition and leads to supra-competitive prices. They sought class

certification under Federal Rule of Civil Procedure 23(b)(3), which 

requires that “questions of law or fact common to class members predominate over any questions affecting only individual members.”

The District Court required them to show (1) that the “antitrust impact” of the violation could be proved at trial through evidence common to the class and (2) that the damages were measurable on a 

classwide basis through a “common methodology.” The court accepted only one of respondents’ four proposed theories of antitrust impact:

that Comcast’s actions lessened competition from “overbuilders,” i.e., 

companies that build competing networks in areas where an incumbent cable company already operates. It then certified the class, finding that the damages from overbuilder deterrence could be calculated 

on a classwide basis, even though respondents’ expert acknowledged

that his regression model did not isolate damages resulting from any 

one of respondents’ theories. In affirming, the Third Circuit refused 

to consider petitioners’ argument that the model failed to attribute

damages to overbuilder deterrence because doing so would require 

reaching the merits of respondents’ claims at the class certification 

stage. 

Held: Respondents’ class action was improperly certified under Rule 

23(b)(3). Pp. 5–11. 
 

 

 

2 COMCAST CORP. v. BEHREND 

Syllabus 

(a) A party seeking to maintain a class action must be prepared to

show that Rule 23(a)’s numerosity, commonality, typicality, and adequacy-of-representation requirements have been met, Wal-Mart 

Stores, Inc. v. Dukes, 564 U. S. ___, ___, and must satisfy through evidentiary proof at least one of Rule 23(b)’s provisions. The same analytical principles govern certification under both Rule 23(a) and Rule

23(b). Courts may have to “ ‘probe behind the pleadings before coming to rest on the certification question,’ and [a] certification is proper 

only if ‘the trial court is satisfied, after a rigorous analysis, that [Rule

23’s] prerequisites . . . have been satisfied.’ ” Ibid. The analysis will

frequently “overlap with the merits of the plaintiff ’s underlying 

claim” because a “ ‘class determination generally involves considerations that are enmeshed in the factual and legal issues comprising

the plaintiff ’s cause of action.’ ” Ibid. Pp. 5–6.

(b) The Third Circuit ran afoul of this Court’s precedents when it 

refused to entertain arguments against respondents’ damages model

that bore on the propriety of class certification simply because they

would also be pertinent to the merits determination. If they prevail, 

respondents would be entitled only to damages resulting from reduced overbuilder competition. A model that does not attempt to

measure only those damages attributable to that theory cannot establish that damages are susceptible of measurement across the entire

class for Rule 23(b)(3) purposes. The lower courts’ contrary reasoning 

flatly contradicts this Court’s cases, which require a determination

that Rule 23 is satisfied, even when that requires inquiry into the 

merits of the claim. Wal-Mart, supra, at ___, and n. 6. Pp. 6–8. 

(c) Under the proper standard for evaluating certification, respondents’ model falls far short of establishing that damages can be measured classwide. The figure respondents’ expert used was calculated 

assuming the validity of all four theories of antitrust impact initially

advanced by respondents. Because the model cannot bridge the differences between supra-competitive prices in general and supracompetitive prices attributable to overbuilder deterrence, Rule 

23(b)(3) cannot authorize treating subscribers in the Philadelphia

cluster as members of a single class. Pp. 8–11. 

655 F. 3d 182, reversed. 

SCALIA, J., delivered the opinion of the Court, in which ROBERTS, 

C. J., and KENNEDY, THOMAS, and ALITO, JJ., joined. GINSBURG and 

BREYER, JJ., filed a dissenting opinion, in which SOTOMAYOR and KAGAN, JJ., joined. 
 

 

_________________ 

_________________ 

Cite as: 569 U. S. ____ (2013) 1 

Opinion of the Court 

NOTICE: This opinion is subject to formal revision before publication in the

preliminary print of the United States Reports. Readers are requested to

notify the Reporter of Decisions, Supreme Court of the United States, Washington, D. C. 20543, of any typographical or other formal errors, in order

that corrections may be made before the preliminary print goes to press. 

SUPREME COURT OF THE UNITED STATES 

No. 11–864 

COMCAST CORPORATION, ET AL., PETITIONERS v.
 

CAROLINE BEHREND ET AL. 

ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF 

APPEALS FOR THE THIRD CIRCUIT
 

[March 27, 2013]

 JUSTICE SCALIA delivered the opinion of the Court. 

The District Court and the Court of Appeals approved

certification of a class of more than 2 million current 

and former Comcast subscribers who seek damages for alleged violations of the federal antitrust laws. We consider 

whether certification was appropriate under Federal Rule

of Civil Procedure 23(b)(3). 

I 

Comcast Corporation and its subsidiaries, petitioners

here, provide cable-television services to residential and 

commercial customers. From 1998 to 2007, petitioners 

engaged in a series of transactions that the parties have 

described as “clustering,” a strategy of concentrating operations within a particular region. The region at issue 

here, which the parties have referred to as the Philadelphia “cluster” or the Philadelphia “Designated Market 

Area” (DMA), includes 16 counties located in Pennsylvania,

Delaware, and New Jersey.1 Petitioners pursued their 

—————— 

1A “Designated Market Area” is a term used by Nielsen Media Research to define a broadcast-television market. Strictly speaking, the 
 

 

2 COMCAST CORP. v. BEHREND 

Opinion of the Court 

clustering strategy by acquiring competitor cable providers in the region and swapping their own systems outside 

the region for competitor systems located in the region.

For instance, in 2001, petitioners obtained Adelphia Communications’ cable systems in the Philadelphia DMA,

along with its 464,000 subscribers; in exchange, petitioners sold to Adelphia their systems in Palm Beach, Florida, 

and Los Angeles, California. As a result of nine clustering transactions, petitioners’ share of subscribers in the region allegedly increased from 23.9 percent in 1998 to 69.5 

percent in 2007. See 264 F. R. D. 150, 156, n. 8, 160 (ED 

Pa. 2010).

The named plaintiffs, respondents here, are subscribers 

to Comcast’s cable-television services. They filed a classaction antitrust suit against petitioners, claiming that 

petitioners entered into unlawful swap agreements, in 

violation of §1 of the Sherman Act, and monopolized or attempted to monopolize services in the cluster, in violation of §2. Ch. 647, 26 Stat. 209, as amended, 15 U. S. C.

§§1, 2. Petitioners’ clustering scheme, respondents contended, harmed subscribers in the Philadelphia cluster by

eliminating competition and holding prices for cable services above competitive levels.

Respondents sought to certify a class under Federal

Rule of Civil Procedure 23(b)(3). That provision permits 

certification only if “the court finds that the questions of

law or fact common to class members predominate over 

any questions affecting only individual members.” The 

District Court held, and it is uncontested here, that to 

meet the predominance requirement respondents had to

show (1) that the existence of individual injury resulting 

from the alleged antitrust violation (referred to as “antitrust impact”) was “capable of proof at trial through

evidence that [was] common to the class rather than indi­

—————— 

Philadelphia DMA comprises 18 counties, not 16. 
Cite as: 569 U. S. ____ (2013) 3 

Opinion of the Court 

vidual to its members”; and (2) that the damages resulting 

from that injury were measurable “on a class-wide basis” 

through use of a “common methodology.” 264 F. R. D., at 

154.2 

Respondents proposed four theories of antitrust impact:

First, Comcast’s clustering made it profitable for Comcast 

to withhold local sports programming from its competitors, resulting in decreased market penetration by direct

broadcast satellite providers. Second, Comcast’s activities 

reduced the level of competition from “overbuilders,” companies that build competing cable networks in areas 

where an incumbent cable company already operates. 

Third, Comcast reduced the level of “benchmark” competition on which cable customers rely to compare prices. 

Fourth, clustering increased Comcast’s bargaining power 

relative to content providers. Each of these forms of impact, respondents alleged, increased cable subscription

rates throughout the Philadelphia DMA.

The District Court accepted the overbuilder theory of 

antitrust impact as capable of classwide proof and rejected 

the rest. Id., at 165, 174, 178, 181. Accordingly, in its 

certification order, the District Court limited respondents’ 

“proof of antitrust impact” to “the theory that Comcast

engaged in anticompetitive clustering conduct, the effect of

which was to deter the entry of overbuilders in the Philadelphia DMA.” App. to Pet. for Cert. 192a–193a.3 

—————— 

2Respondents sought certification for the following class: “All cable

television customers who subscribe or subscribed at any times since 

December 1, 1999, to the present to video programming services (other

than solely to basic cable services) from Comcast, or any of its subsidiaries or affiliates in Comcast’s Philadelphia cluster.” App. 35a. 3The District Court did not hold that the three alternative theories of 

liability failed to establish antitrust impact, but merely that those

theories could not be determined in a manner common to all the class 

plaintiffs. The other theories of liability may well be available for

the plaintiffs to pursue as individual actions. Any contention that the 

plaintiffs should be allowed to recover damages attributable to all four 
 

4 COMCAST CORP. v. BEHREND 

Opinion of the Court 

The District Court further found that the damages

resulting from overbuilder-deterrence impact could be

calculated on a classwide basis. To establish such damages, respondents had relied solely on the testimony of Dr. 

James McClave. Dr. McClave designed a regression model 

comparing actual cable prices in the Philadelphia DMA 

with hypothetical prices that would have prevailed but 

for petitioners’ allegedly anticompetitive activities. The 

model calculated damages of $875,576,662 for the entire

class. App. 1388a (sealed). As Dr. McClave acknowledged, 

however, the model did not isolate damages resulting 

from any one theory of antitrust impact. Id., at 189a– 

190a. The District Court nevertheless certified the class. 

A divided panel of the Court of Appeals affirmed. On 

appeal, petitioners contended the class was improperly

certified because the model, among other shortcomings, 

failed to attribute damages resulting from overbuilder 

deterrence, the only theory of injury remaining in the case. 

The court refused to consider the argument because, in its

view, such an “attac[k] on the merits of the methodology

[had] no place in the class certification inquiry.” 655 F. 3d 

182, 207 (CA3 2011). The court emphasized that, “[a]t

the class certification stage,” respondents were not required 

to “tie each theory of antitrust impact to an exact calculation of damages.” Id., at 206. According to the court, it

had “not reached the stage of determining on the merits 

whether the methodology is a just and reasonable inference or speculative.” Ibid. Rather, the court said, respondents must “assure us that if they can prove antitrust 

impact, the resulting damages are capable of measurement and will not require labyrinthine individual calcula­

—————— 

theories in this class action would erroneously suggest one of two 

things—either that the plaintiffs may also recover such damages in 

individual actions or that they are precluded from asserting those

theories in individual actions. 
 

 

 

 

Cite as: 569 U. S. ____ (2013) 5 

Opinion of the Court 

tions.” Ibid. In the court’s view, that burden was met 

because respondents’ model calculated “supra-competitive

prices regardless of the type of anticompetitive conduct.” 

Id., at 205. 

We granted certiorari. 567 U. S. ___ (2012).4 

II 

The class action is “an exception to the usual rule that

litigation is conducted by and on behalf of the individual 

named parties only.” Califano v. Yamasaki, 442 U. S. 682, 

700–701 (1979). To come within the exception, a party 

seeking to maintain a class action “must affirmatively

demonstrate his compliance” with Rule 23. Wal-Mart 

Stores, Inc. v. Dukes, 564 U. S. ___, ___ (2011) (slip op., at 

10). The Rule “does not set forth a mere pleading standard.” Ibid. Rather, a party must not only “be prepared to 

prove that there are in fact sufficiently numerous parties,

common questions of law or fact,” typicality of claims or

defenses, and adequacy of representation, as required by 

Rule 23(a). Ibid. The party must also satisfy through 

evidentiary proof at least one of the provisions of Rule 

—————— 

4The question presented reads: “Whether a district court may certify 

a class action without resolving whether the plaintiff class had introduced admissible evidence, including expert testimony, to show that the

case is susceptible to awarding damages on a class-wide basis.” 567 

U. S., at ___. Respondents contend that petitioners forfeited their 

ability to answer this question in the negative because they did not 

make an objection to the admission of Dr. McClave’s testimony under 

the Federal Rules of Evidence. See Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U. S. 579 (1993). Such a forfeit would make it 

impossible for petitioners to argue that Dr. McClave’s testimony was

not “admissible evidence” under the Rules; but it does not make it 

impossible for them to argue that the evidence failed “to show that the

case is susceptible to awarding damages on a class-wide basis.” Petitioners argued below, and continue to argue here, that certification was

improper because respondents had failed to establish that damages

could be measured on a classwide basis. That is the question we 

address here. 
 

 

6 COMCAST CORP. v. BEHREND 

Opinion of the Court 

23(b). The provision at issue here is Rule 23(b)(3), which

requires a court to find that “the questions of law or fact

common to class members predominate over any questions 

affecting only individual members.”

Repeatedly, we have emphasized that it “‘may be necessary for the court to probe behind the pleadings before 

coming to rest on the certification question,’ and that 

certification is proper only if ‘the trial court is satisfied,

after a rigorous analysis, that the prerequisites of Rule 

23(a) have been satisfied.’” Ibid. (quoting General Telephone Co. of Southwest v. Falcon, 457 U. S. 147, 160–161 

(1982)). Such an analysis will frequently entail “overlap 

with the merits of the plaintiff ’s underlying claim.” 564 

U. S., at ___ (slip op., at 10). That is so because the “‘class 

determination generally involves considerations that are 

enmeshed in the factual and legal issues comprising the 

plaintiff ’s cause of action.’” Ibid. (quoting Falcon, supra, 

at 160).

The same analytical principles govern Rule 23(b). If 

anything, Rule 23(b)(3)’s predominance criterion is even 

more demanding than Rule 23(a). Amchem Products, Inc. 

v. Windsor, 521 U. S. 591, 623–624 (1997). Rule 23(b)(3),

as an “‘adventuresome innovation,’” is designed for situations “‘in which “class-action treatment is not as clearly 

called for.”’” Wal-Mart, supra, at ___ (slip op., at 22) 

(quoting Amchem, 521 U. S., at 614–615). That explains

Congress’s addition of procedural safeguards for (b)(3) 

class members beyond those provided for (b)(1) or (b)(2)

class members (e.g., an opportunity to opt out), and the 

court’s duty to take a “‘close look’” at whether common

questions predominate over individual ones. Id., at 615. 

III 

Respondents’ class action was improperly certified under Rule 23(b)(3). By refusing to entertain arguments

against respondents’ damages model that bore on the 
Cite as: 569 U. S. ____ (2013) 7 

Opinion of the Court 

propriety of class certification, simply because those arguments would also be pertinent to the merits determination, the Court of Appeals ran afoul of our precedents 

requiring precisely that inquiry. And it is clear that, 

under the proper standard for evaluating certification,

respondents’ model falls far short of establishing that

damages are capable of measurement on a classwide basis. 

Without presenting another methodology, respondents

cannot show Rule 23(b)(3) predominance: Questions of 

individual damage calculations will inevitably overwhelm 

questions common to the class. This case thus turns on 

the straightforward application of class-certification principles; it provides no occasion for the dissent’s extended 

discussion, post, at 5–11 (GINSBURG and BREYER, JJ., 

dissenting), of substantive antitrust law. 

A 

We start with an unremarkable premise. If respondents

prevail on their claims, they would be entitled only to

damages resulting from reduced overbuilder competition, 

since that is the only theory of antitrust impact accepted 

for class-action treatment by the District Court. It follows 

that a model purporting to serve as evidence of damages in

this class action must measure only those damages attributable to that theory. If the model does not even attempt to do that, it cannot possibly establish that damages 

are susceptible of measurement across the entire class for 

purposes of Rule 23(b)(3). Calculations need not be exact, 

see Story Parchment Co. v. Paterson Parchment Paper Co., 

282 U. S. 555, 563 (1931), but at the class-certification 

stage (as at trial), any model supporting a “plaintiff ’s 

damages case must be consistent with its liability case, 

particularly with respect to the alleged anticompetitive

effect of the violation.” ABA Section of Antitrust Law, 

Proving Antitrust Damages: Legal and Economic Issues 

57, 62 (2d ed. 2010); see, e.g., Image Tech. Servs. v. East-
 

 

8 COMCAST CORP. v. BEHREND 

Opinion of the Court 

man Kodak Co., 125 F. 3d 1195, 1224 (CA9 1997). And for 

purposes of Rule 23, courts must conduct a “‘rigorous

analysis’” to determine whether that is so. Wal-Mart, 

supra, at ___ (slip op., at 10). 

The District Court and the Court of Appeals saw no 

need for respondents to “tie each theory of antitrust impact” to a calculation of damages. 655 F. 3d, at 206. That, 

they said, would involve consideration of the “merits”

having “no place in the class certification inquiry.” Id., 

at 206–207. That reasoning flatly contradicts our cases 

requiring a determination that Rule 23 is satisfied, even 

when that requires inquiry into the merits of the claim. 

Wal-Mart, supra, at ___, and n. 6 (slip op., at 10–11, and 

n. 6). The Court of Appeals simply concluded that respondents “provided a method to measure and quantify 

damages on a classwide basis,” finding it unnecessary to

decide “whether the methodology [was] a just and reasonable inference or speculative.” 655 F. 3d, at 206. Under 

that logic, at the class-certification stage any method of 

measurement is acceptable so long as it can be applied 

classwide, no matter how arbitrary the measurements

may be. Such a proposition would reduce Rule 23(b)(3)’s

predominance requirement to a nullity. 

B 

There is no question that the model failed to measure 

damages resulting from the particular antitrust injury

on which petitioners’ liability in this action is premised.5 

—————— 

5The dissent is of the view that what an econometric model proves is 

a “question of fact” on which we will not “undertake to review concurrent findings . . . by two courts below in the absence of a very obvious 

and exceptional showing of error.” Post, at 9 (quoting United States v. 

Virginia, 518 U. S. 515, 589, n. 5 (1996) (SCALIA, J., dissenting) (internal quotation marks omitted)). To begin with, neither of the courts 

below found that the model established damages attributable to overbuilding alone. Second, while the data contained within an econometric 

model may well be “questions of fact” in the relevant sense, what those 
 

Cite as: 569 U. S. ____ (2013) 9 

Opinion of the Court 

The scheme devised by respondents’ expert, Dr. McClave,

sought to establish a “but for” baseline—a figure that 

would show what the competitive prices would have been 

if there had been no antitrust violations. Damages would 

then be determined by comparing to that baseline what

the actual prices were during the charged period. The 

“but for” figure was calculated, however, by assuming a 

market that contained none of the four distortions that 

respondents attributed to petitioners’ actions. In other 

words, the model assumed the validity of all four theories 

of antitrust impact initially advanced by respondents: 

decreased penetration by satellite providers, overbuilder 

deterrence, lack of benchmark competition, and increased 

bargaining power. At the evidentiary hearing, Dr.

McClave expressly admitted that the model calculated 

damages resulting from “the alleged anticompetitive 

conduct as a whole” and did not attribute damages to 

any one particular theory of anticompetitive impact. App. 

189a–190a, 208a. 

This methodology might have been sound, and might 

have produced commonality of damages, if all four of those 

alleged distortions remained in the case. But as Judge 

Jordan’s partial dissent pointed out: 

“[B]ecause the only surviving theory of antitrust impact is that clustering reduced overbuilding, for Dr.

McClave’s comparison to be relevant, his benchmark 

counties must reflect the conditions that would have 

prevailed in the Philadelphia DMA but for the alleged

reduction in overbuilding. In all respects unrelated to 

reduced overbuilding, the benchmark counties should 

—————— 

data prove is no more a question of fact than what our opinions hold.

And finally, even if it were a question of fact, concluding that the model 

here established damages attributable to overbuilding alone would be

“obvious[ly] and exceptional[ly]” erroneous. 
 

 

10 COMCAST CORP. v. BEHREND 

Opinion of the Court 

reflect the actual conditions in the Philadelphia DMA,

or else the model will identify ‘damages’ that are not 

the result of reduced overbuilding, or, in other words, 

that are not the certain result of the wrong.” 655 

F. 3d, at 216 (internal quotation marks omitted). 

The majority’s only response to this was that “[a]t the

class certification stage we do not require that Plaintiffs 

tie each theory of antitrust impact to an exact calculation 

of damages, but instead that they assure us that if they 

can prove antitrust impact, the resulting damages are 

capable of measurement and will not require labyrinthine 

individual calculations.” Id., at 206. But such assurance 

is not provided by a methodology that identifies damages 

that are not the result of the wrong. For all we know, 

cable subscribers in Gloucester County may have been

overcharged because of petitioners’ alleged elimination of 

satellite competition (a theory of liability that is not capable of classwide proof ); while subscribers in Camden 

County may have paid elevated prices because of petitioners’ 

increased bargaining power vis-à-vis content providers 

(another theory that is not capable of classwide proof ); 

while yet other subscribers in Montgomery County may 

have paid rates produced by the combined effects of multiple forms of alleged antitrust harm; and so on. The permutations involving four theories of liability and 2 million 

subscribers located in 16 counties are nearly endless.

In light of the model’s inability to bridge the differences 

between supra-competitive prices in general and supracompetitive prices attributable to the deterrence of overbuilding, Rule 23(b)(3) cannot authorize treating subscribers within the Philadelphia cluster as members of a single 

class.6 Prices whose level above what an expert deems 

—————— 

6We might add that even if the model had identified subscribers who

paid more solely because of the deterrence of overbuilding, it still would

not have established the requisite commonality of damages unless it 
 

Cite as: 569 U. S. ____ (2013) 11 

Opinion of the Court 

“competitive” has been caused by factors unrelated to an

accepted theory of antitrust harm are not “anticompetitive” in any sense relevant here. “The first step in a damages study is the translation of the legal theory of the 

harmful event into an analysis of the economic impact of 

that event.” Federal Judicial Center, Reference Manual on 

Scientific Evidence 432 (3d ed. 2011) (emphasis added).

The District Court and the Court of Appeals ignored that

first step entirely.

The judgment of the Court of Appeals for the Third Circuit is reversed. 

It is so ordered. 

—————— 

plausibly showed that the extent of overbuilding (absent deterrence) 

would have been the same in all counties, or that the extent is irrelevant to effect upon ability to charge supra-competitive prices. 
_________________ 

_________________ 

Cite as: 569 U. S. ____ (2013) 1 

GINSBURG and BREYER, JJ., dissenting 

SUPREME COURT OF THE UNITED STATES 

No. 11–864 

COMCAST CORPORATION, ET AL., PETITIONERS v.
 

CAROLINE BEHREND ET AL. 

ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF 

APPEALS FOR THE THIRD CIRCUIT
 

[March 27, 2013]

 JUSTICE GINSBURG and JUSTICE BREYER, with whom 

JUSTICE SOTOMAYOR and JUSTICE KAGAN join, dissenting. 

Today the Court reaches out to decide a case hardly fit

for our consideration. On both procedural and substantive 

grounds, we dissent. 

I 

This case comes to the Court infected by our misguided

reformulation of the question presented. For that reason 

alone, we would dismiss the writ of certiorari as improvidently granted. 

Comcast sought review of the following question:

“[W]hether a district court may certify a class action without resolving ‘merits arguments’ that bear on [Federal

Rule of Civil Procedure] 23’s prerequisites for certification, including whether purportedly common issues predominate over individual ones under Rule 23(b)(3).” Pet. 

for Cert. i. We granted review of a different question:

“Whether a district court may certify a class action without resolving whether the plaintiff class has introduced 

admissible evidence, including expert testimony, to show 

that the case is susceptible to awarding damages on a

class-wide basis.” 567 U. S. ___ (2012) (emphasis added). 

Our rephrasing shifted the focus of the dispute from the 

District Court’s Rule 23(b)(3) analysis to its attention (or 
 

 

 

 

2 COMCAST CORP. v. BEHREND 

GINSBURG and BREYER, JJ., dissenting 

lack thereof) to the admissibility of expert testimony. The 

parties, responsively, devoted much of their briefing to the 

question whether the standards for admissibility of expert 

evidence set out in Federal Rule of Evidence 702 and 

Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U. S. 

579 (1993), apply in class certification proceedings. See 

Brief for Petitioners 35–49; Brief for Respondents 24–37. 

Indeed, respondents confirmed at oral argument that they 

understood our rewritten question to center on admissibility, not Rule 23(b)(3). See, e.g., Tr. of Oral Arg. 25.

As it turns out, our reformulated question was inapt. To 

preserve a claim of error in the admission of evidence, a 

party must timely object to or move to strike the evidence.

Fed. Rule Evid. 103(a)(1). In the months preceding the 

District Court’s class certification order, Comcast did not 

object to the admission of Dr. McClave’s damages model

under Rule 702 or Daubert. Nor did Comcast move to 

strike his testimony and expert report. Consequently,

Comcast forfeited any objection to the admission of Dr.

McClave’s model at the certification stage. At this late 

date, Comcast may no longer argue that respondents’ 

damages evidence was inadmissible. 

Comcast’s forfeiture of the question on which we granted 

review is reason enough to dismiss the writ as improvidently granted. See Rogers v. United States, 522 U. S. 

252, 259 (1998) (O’Connor, J., concurring in result) (“[W]e 

ought not to decide the question if it has not been cleanly 

presented.”); The Monrosa v. Carbon Black Export, Inc., 

359 U. S. 180, 183 (1959) (dismissal appropriate in light 

of “circumstances . . . not fully apprehended at the time

certiorari was granted” (internal quotation marks omitted)). The Court, however, elects to evaluate whether respondents “failed to show that the case is susceptible to 

awarding damages on a class-wide basis.” Ante, at 5, n. 4 

(internal quotation marks omitted). To justify this second

revision of the question presented, the Court observes that 
 

Cite as: 569 U. S. ____ (2013) 3 

GINSBURG and BREYER, JJ., dissenting 

Comcast “argued below, and continue[s] to argue here,

that certification was improper because respondents had

failed to establish that damages could be measured on a 

classwide basis.” Ibid. And so Comcast did, in addition to 

endeavoring to address the question on which we granted 

review. By treating the first part of our reformulated

question as though it did not exist, the Court is hardly fair 

to respondents.

Abandoning the question we instructed the parties to

brief does “not reflect well on the processes of the Court.” 

Redrup v. New York, 386 U. S. 767, 772 (1967) (Harlan, J., 

dissenting). Taking their cue from our order, respondents 

did not train their energies on defending the District

Court’s finding of predominance in their briefing or at oral 

argument. The Court’s newly revised question, focused on

predominance, phrased only after briefing was done, left 

respondents without an unclouded opportunity to air the 

issue the Court today decides against them. And by resolving a complex and fact-intensive question without the

benefit of full briefing, the Court invites the error into

which it has fallen. See infra, at 5–11. 

II 

While the Court’s decision to review the merits of the 

District Court’s certification order is both unwise and unfair to respondents, the opinion breaks no new ground on

the standard for certifying a class action under Federal 

Rule of Civil Procedure 23(b)(3). In particular, the decision should not be read to require, as a prerequisite to 

certification, that damages attributable to a classwide 

injury be measurable “‘on a class-wide basis.’” See ante, 

at 2–3 (acknowledging Court’s dependence on the absence 

of contest on the matter in this case); Tr. of Oral Arg. 41.

To gain class-action certification under Rule 23(b)(3),

the named plaintiff must demonstrate, and the District 

Court must find, “that the questions of law or fact common 
 

 

4 COMCAST CORP. v. BEHREND 

GINSBURG and BREYER, JJ., dissenting 

to class members predominate over any questions affecting only individual members.” This predominance requirement is meant to “tes[t] whether proposed classes are

sufficiently cohesive to warrant adjudication by representation,” Amchem Products, Inc. v. Windsor, 521 U. S. 591, 

623 (1997), but it scarcely demands commonality as to all 

questions. See 7AA C. Wright, A. Miller, & M. Kane,

Federal Practice and Procedure §1778, p. 121 (3d ed. 2005) 

(hereinafter Wright, Miller, & Kane). In particular, when

adjudication of questions of liability common to the class

will achieve economies of time and expense, the predominance standard is generally satisfied even if damages are

not provable in the aggregate. See Advisory Committee’s

1966 Notes on Fed. Rule Civ. Proc. 23, 28 U. S. C. App.,

p. 141 (“[A] fraud perpetrated on numerous persons by 

the use of similar misrepresentations may be an appealing

situation for a class action, and it may remain so despite 

the need, if liability is found, for separate determination of 

the damages suffered by individuals within the class.”); 

7AA Wright, Miller, & Kane §1781, at 235–237.* 

Recognition that individual damages calculations do not 

preclude class certification under Rule 23(b)(3) is well nigh 

universal. See 2 W. Rubenstein, Newberg on Class Actions §4:54, p. 205 (5th ed. 2012) (ordinarily, “individual

damage[s] calculations should not scuttle class certification under Rule 23(b)(3)”). Legions of appellate decisions

across a range of substantive claims are illustrative. See, 

e.g., Tardiff v. Knox County, 365 F. 3d 1, 6 (CA1 2004) 

(Fourth Amendment); Chiang v. Veneman, 385 F. 3d 256, 

273 (CA3 2004) (Equal Credit Opportunity Act); Bertulli v. 

—————— 

*A class may be divided into subclasses for adjudication of damages.

Fed. Rule Civ. Proc. 23(c)(4)–(5). Or, at the outset, a class may be

certified for liability purposes only, leaving individual damages calculations to subsequent proceedings. See 2 W. Rubenstein, Newberg on

Class Actions §4:54, pp. 206–208 (5th ed. 2012). Further, a certification 

order may be altered or amended as the case unfolds. Rule 23(c)(1)(C). 
 

Cite as: 569 U. S. ____ (2013) 5 

GINSBURG and BREYER, JJ., dissenting 

Independent Assn. of Continental Pilots, 242 F. 3d 290, 

298 (CA5 2001) (Labor-Management Reporting and Disclosure Act and Railway Labor Act); Beattie v. CenturyTel, 

Inc., 511 F. 3d 554, 564–566 (CA6 2007) (Federal Communications Act); Arreola v. Godinez, 546 F. 3d 788, 801 (CA7 

2008) (Eighth Amendment). Antitrust cases, which typically involve common allegations of antitrust violation, 

antitrust impact, and the fact of damages, are classic

examples. See In re Visa Check/MasterMoney Antitrust 

Litigation, 280 F. 3d 124, 139–140 (CA2 2001). See also 

2A P. Areeda, H. Hovenkamp, R. Blair, & C. Durrance,

Antitrust Law ¶331, p. 56 (3d ed. 2007) (hereinafter 

Areeda & Hovenkamp); 6 A. Conte & H. Newberg, Newberg on Class Actions §18:27, p. 91 (4th ed. 2002). As 

this Court has rightly observed, “[p]redominance is a test

readily met” in actions alleging “violations of the antitrust

laws.” Amchem, 521 U. S., at 625. 

The oddity of this case, in which the need to prove

damages on a classwide basis through a common methodology was never challenged by respondents, see Brief for 

Plaintiffs-Appellees in No. 10–2865 (CA3), pp. 39–40, is a 

further reason to dismiss the writ as improvidently granted. 

The Court’s ruling is good for this day and case only. 

In the mine run of cases, it remains the “black letter rule” 

that a class may obtain certification under Rule 23(b)(3)

when liability questions common to the class predominate

over damages questions unique to class members. 2 Rubenstein, supra, §4:54, at 208. 

III 

Incautiously entering the fray at this interlocutory

stage, the Court sets forth a profoundly mistaken view of 

antitrust law. And in doing so, it relies on its own version 

of the facts, a version inconsistent with factual findings

made by the District Court and affirmed by the Court of 

Appeals. 
 

6 COMCAST CORP. v. BEHREND 

GINSBURG and BREYER, JJ., dissenting 

A 

To understand the antitrust problem, some (simplified) 

background discussion is necessary. Plaintiffs below, respondents here, alleged that Comcast violated §§1 and 2

of the Sherman Act. See 15 U. S. C. §§1, 2. For present

purposes, the §2 claim provides the better illustration. A 

firm is guilty of monopolization under §2 if the plaintiff 

proves (1) “the possession of monopoly power in the relevant market” and (2) “the willful acquisition or maintenance of that power[,] as distinguished from growth or 

development as a consequence of a superior product, business acumen, or historic accident.” United States v. 

Grinnell Corp., 384 U. S. 563, 570–571 (1966). A private

plaintiff seeking damages must also show that (3) the 

monopolization caused “injur[y].” 15 U. S. C. §15. We 

have said that antitrust injuries must be “of the type the 

antitrust laws were intended to prevent and that flo[w] 

from that which makes defendants’ acts unlawful.” Atlantic Richfield Co. v. USA Petroleum Co., 495 U. S. 328, 334 

(1990) (quoting Brunswick Corp. v. Pueblo Bowl-O-Mat, 

Inc., 429 U. S. 477, 489 (1977)). See 2A Areeda & Hovenkamp ¶391a, at 320 (To prove antitrust injury, “[a] 

private plaintiff must identify the economic rationale for a 

business practice’s illegality under the antitrust laws and 

show that its harm flows from whatever it is that makes 

the practice unlawful.”). 

As plaintiffs below, respondents attempted to meet

these requirements by showing that (1) Comcast obtained

a 60% or greater share of the Philadelphia market, and 

that its share provides it with monopoly power; (2) Comcast acquired its share through exclusionary conduct 

consisting of a series of mergers with competitors and 

“swaps” of customers and locations; and (3) Comcast consequently injured respondents by charging them supracompetitive prices.

If, as respondents contend, Philadelphia is a separate 
 

 

Cite as: 569 U. S. ____ (2013) 7 

GINSBURG and BREYER, JJ., dissenting 

well-defined market, and the alleged exclusionary conduct 

permitted Comcast to obtain a market share of at least 

60%, then proving the §2 violation may not be arduous. 

As a point of comparison, the government considers a

market shared by four firms, each of which has 25% market share, to be “highly concentrated.” Dept. of Justice &

Federal Trade Commission, Horizontal Merger Guidelines

§5.3, p. 19 (2010). A market, such as the one alleged by

respondents, where one firm controls 60% is far worse. 

See id., §5.3, at 18–19, and n. 9 (using a concentration

index that determines a market’s concentration level by

summing the squares of each firm’s market share, one 

firm with 100% yielding 10,000, five firms with 20% each 

yielding 2000, while a market where one firm accounts for 

60% yields an index number of at least 3,600). The Guidelines, and any standard antitrust treatise, explain why 

firms in highly concentrated markets normally have the

power to raise prices significantly above competitive levels. See, e.g., 2B Areeda & Hovenkamp ¶503, at 115. 

B 

So far there is agreement. But consider the last matter 

respondents must prove: Can they show that Comcast 

injured them by charging higher prices? After all, a firm 

with monopoly power will not necessarily exercise that

power by charging higher prices. It could instead act less 

competitively in other ways, such as by leading the quiet 

life. See J. Hicks, Annual Survey of Economic Theory: The 

Theory of Monopoly, 3 Econometrica 1, 8 (1935) (“The best 

of all monopoly profits is a quiet life.”). 

It is at this point that Dr. McClave’s model enters the 

scene. His model first selects a group of comparable 

outside-Philadelphia “benchmark” counties, where Comcast 

enjoyed a lower market share (and where satellite broadcasting accounted for more of the local business). Using

multiple regression analysis, McClave’s model measures 
 

8 COMCAST CORP. v. BEHREND 

GINSBURG and BREYER, JJ., dissenting 

the effect of the anticompetitive conduct by comparing

the class counties to the benchmark counties. The model 

concludes that the prices Philadelphia area consumers 

would have paid had the Philadelphia counties shared 

the properties of the benchmark counties (including a

diminished Comcast market share), would have been

13.1% lower than those they actually paid. Thus, the model 

provides evidence that Comcast’s anticompetitive conduct,

which led to a 60% market share, caused the class to 

suffer injuriously higher prices. 

C 

1 

The special antitrust-related difficulty present here

stems from the manner in which respondents attempted 

to prove their antitrust injuries. They proffered four

“non-exclusive mechanisms” that allegedly “cause[d] the 

high prices” in the Philadelphia area. App. 403a. Those four 

theories posit that (1) due to Comcast’s acquisitions of

competitors, customers found it more difficult to compare

prices; (2) one set of potential competitors, namely Direct

Broadcast Satellite companies, found it more difficult to 

obtain access to local sports broadcasts and consequently

decided not to enter the Philadelphia market; (3) Comcast’s ability to obtain programming material at lower 

prices permitted it to raise prices; and (4) a number of 

potential competitors (called “overbuilders”), whose presence in the market would have limited Comcast’s power to

raise prices, were ready to enter some parts of the market

but decided not to do so in light of Comcast’s anticompetitive conduct. 264 F. R. D. 150, 161–162 (ED Pa. 2010).

For reasons not here relevant, the District Court found 

the first three theories inapplicable and limited the 

liability-phase proof to the “overbuilder” theory. See App.

to Pet. for Cert. 192a–193a. It then asked the parties to

brief whether doing so had any impact on the viability of 
 

 

Cite as: 569 U. S. ____ (2013) 9 

GINSBURG and BREYER, JJ., dissenting 

McClave’s model as a measure of classwide damages. See 

264 F. R. D., at 190. After considering the parties’ arguments, the District Court found that striking the three 

theories “does not impeach Dr. McClave’s damages model” 

because “[a]ny anticompetitive conduct is reflected in the

[higher Philadelphia] price [which Dr. McClave’s model 

determines], not in the [the model’s] selection of the 

comparison counties, [i.e., the lower-price ‘benchmark 

counties’ with which the Philadelphia area prices were

compared].” Id., at 190–191. The court explained that

“whether or not we accepted all [four] . . . theories . . . is 

inapposite to Dr. McClave’s methods of choosing benchmarks.” Ibid. On appeal, the Third Circuit held that this

finding was not an abuse of discretion. 655 F. 3d 182, 207 

(2011). 

2 

The Court, however, concludes that “the model failed to 

measure damages resulting from the particular antitrust

injury on which petitioners’ liability in this action is premised.” Ante, at 8. To reach this conclusion the Court must 

consider fact-based matters, namely what this econometric 

multiple-regression model is about, what it proves, and 

how it does so. And it must overturn two lower courts’ 

related factual findings to the contrary.

We are normally “reluctant to disturb findings of fact in

which two courts below have concurred.” United States v. 

Doe, 465 U. S. 605, 614 (1984). See also United States v. 

Virginia, 518 U. S. 515, 589, n. 5 (1996) (SCALIA, J., dissenting) (noting “our well-settled rule that we will not 

‘undertake to review concurrent findings of fact by two

courts below in the absence of a very obvious and exceptional showing of error’” (quoting Graver Tank & Mfg. Co. 

v. Linde Air Products Co., 336 U. S. 271, 275 (1949))). 

Here, the District Court found McClave’s econometric 

model capable of measuring damages on a classwide basis, 
 

10 COMCAST CORP. v. BEHREND 

GINSBURG and BREYER, JJ., dissenting 

even after striking three of the injury theories. 264 

F. R. D., at 190–191. Contrary to the Court’s characterization, see ante, at 8–9, n. 5, this was not a legal conclusion 

about what the model proved; it was a factual finding 

about how the model worked. Under our typical practice,

we should leave that finding alone.

In any event, as far as we can tell, the lower courts were 

right. On the basis of the record as we understand it, the 

District Court did not abuse its discretion in finding that

McClave’s model could measure damages suffered by the 

class—even if the damages were limited to those caused by 

deterred overbuilding. That is because respondents alleged that Comcast’s anticompetitive conduct increased 

Comcast’s market share (and market power) by deterring 

potential entrants, in particular, overbuilders, from entering the Philadelphia area market. See App. 43a–66a. By

showing that this was so, respondents’ proof tends to show 

the same in respect to other entrants. The overbuilders’ 

failure to enter deprives the market of the price discipline

that their entry would have provided in other parts via

threat of the overbuilders’ expansion or that of others 

potentially led on by their example. Indeed, in the District 

Court, Comcast argued that the three other theories, 

i.e., the three rejected theories, had no impact on prices. 

See 264 F. R. D., at 166, 176, 180–181. If Comcast was 

right, then the damages McClave’s model found must 

have stemmed exclusively from conduct that deterred new 

entry, say from “overbuilders.” Not surprisingly, the

Court offers no support at all for its contrary conclusion, 

namely, that the District Court’s finding was “ ‘obvious[ly] 

and exceptional[ly]’ erroneous.” Ante, at 8–9, n. 5 (quoting 

Virginia, 518 U. S., at 589, n. 5 (SCALIA, J., dissenting)). 

We are particularly concerned about the matter because

the Court, in reaching its contrary conclusion, makes 

broad statements about antitrust law that it could not 

mean to apply in other cases. The Court begins with what 
 

 

Cite as: 569 U. S. ____ (2013) 11 

GINSBURG and BREYER, JJ., dissenting 

it calls an “unremarkable premise” that respondents could 

be “entitled only to damages resulting from reduced overbuilder competition.” Ante, at 7. In most §2 cases, however, the Court’s starting place would seem remarkable, not 

“unremarkable.” 

Suppose in a different case a plaintiff were to prove that

Widget, Inc. has obtained, through anticompetitive means, 

a 90% share of the California widget market. Suppose the

plaintiff also proves that the two small remaining firms—

one in Ukiah, the other in San Diego—lack the capacity to 

expand their widget output to the point where that possibility could deter Widget, Inc. from raising its prices. 

Suppose further that the plaintiff introduces a model that

shows California widget prices are now twice those in

every other State, which, the model concludes is (after 

accounting for other possible reasons) the result of lack of 

competition in the California widget market. Why would a 

court hearing that case restrict damages solely to customers in the vicinity of Ukiah and San Diego?

Like the model in this example, Dr. McClave’s model 

does not purport to show precisely how Comcast’s conduct 

led to higher prices in the Philadelphia area. It simply

shows that Comcast’s conduct brought about higher prices. 

And it measures the amount of subsequent harm. 

* * * 

Because the parties did not fully argue the question the 

Court now answers, all Members of the Court may lack a

complete understanding of the model or the meaning of 

related statements in the record. The need for focused 

argument is particularly strong here where, as we have 

said, the underlying considerations are detailed, technical, 

and fact-based. The Court departs from our ordinary

practice, risks inaccurate judicial decisionmaking, and is

unfair to respondents and the courts below. For these reasons, we would not disturb the Court of Appeals’ judgment 
 

12 COMCAST CORP. v. BEHREND 

GINSBURG and BREYER, JJ., dissenting 

and, instead, would dismiss the writ as improvidently 

granted.