Scientific & Technical Review

Panel Final Report for

OSAC 2022-S-0030

Standard for Methodology in

Bloodstain Pattern Analysis

Organization of Scientific Area Committees (OSAC) for Forensic Science
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STRP Final Report

OSAC 2022-S-0030

Standard for Methodology in Bloodstain

Pattern Analysis

Organization of Scientific Area Committees (OSAC) for Forensics Science

April 18, 2023

Disclaimer:

This report was produced by an independent Scientific and Technical Review Panel (STRP). The

views expressed in the report do not necessarily reflect the views or policies of the U.S.

Government. Visit the OSAC website for more information on OSAC’s STRP process.

Scientific & Technical Review Panel Members

• Daniel Attinger, Struo, LLC

• Madeline Ausdemore, Los Alamos National Laboratory

• Jodi Corsi, Metropolitan Detroit Forensic Laboratory

• Stephen Henderson, University of Oklahoma

• Kenneth Martin, Bevel, Gardner and Associates, Inc.

• Guy Nutter, Michigan State Police: Northville Forensic Lab

• LeeAnn Singley, Grayson Singley Associates

• William Thompson, University of California, Irvine

• Kevin Winer, Kansas City Police Crime Lab
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Report Summary:

The Scientific and Technical Review Panel (STRP) for “Standard for Methodology in Bloodstain

Pattern Analysis” is an independent panel appointed by the National Institute of Standards and

Technology (NIST). A STRP is established with a range of experts to consider how well a

standard meets the needs of the forensic science, law enforcement, and legal communities, and to

recommend improvements to the standards under review. The STRP appreciates the efforts of

Nicole Blackwell, Bloodstain Pattern Analysis Subcommittee member, while serving as the

subcommittee liaison to this STRP during the review process.

The STRP began its review process with a kickoff meeting on April 11, 2022, and concluded

with this STRP final report. The panel reviewed the draft standard and prepared comments for

the Bloodstain Pattern Analysis Subcommittee.

Report Components:

The STRP reviewed this draft standard against OSAC’s STRP Instructions for Review which

include the following content areas: scientific and technical merit, human factors, quality

assurance, scope and purpose, terminology, method description and reporting results. The details

below contain a brief description of each reviewed content area and the STRP’s assessment of

how that content was addressed in the Draft OSAC Proposed Standard.

1. Scientific and Technical Merit: OSAC-approved standards must have strong scientific

foundations so that the methods practitioners employ are scientifically valid, and the

resulting claims are trustworthy. In addition, standards for methods or interpretation of

results must include the expression and communication of the uncertainties in measurements

or other results.

1.1 Consensus View

The STRP noted that the proposed standard delineates a standard methodology
when conducting a bloodstain pattern analysis. It covers the process to be followed

when examining bloodstains and bloodstain patterns to determine the importance

of their presence or absence, and the importance of those determinations in regard

to the scope or reason for the examination. This standard provides a sound

scientific methodology, which will result in reliable and verifiable results thereby

instilling confidence among our stakeholders.

1.2 Minority View

The Consensus View is an overly optimistic view that does not acknowledge the

limited scope of the standard.

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1.3 Additional Comment Received After Voting

With regard to the bibliography, an STRP member believes it is important to add

the following references that relate to the accuracy of bloodstain pattern analysis

(BPA) and its susceptibility to bias, and therefore help explain what motivated the

document and why it makes the recommendations that it does:

1. R. Austin Hicklin, Kevin R. Winer, Paul E. Kish, Connie L. Parks, William

Chapman, Kensley Dunagan, Nicole Richetelli, EricG. Epstein, Madeline A.

Ausdemore and Thomas A. Busey, Accuracy and Reproducibility of Conclusions

by Forensic Bloodstain Pattern Analysts, Forensic Science International, (2021).

doi:https://doi.org/10.1016/j.forsciint.2021.110856.

2. M.C. Taylor, T.L. Laber, P.E. Kish, G. Owens, N.K.P. Osborne, The

Reliability of Pattern Classification in Bloodstain Pattern Analysis, Part 1:

Bloodstain Patterns on Rigid Non-absorbent Surfaces, J. Forensic Sci. 61 (2016)

922–927. https://doi.org/10.1111/1556-4029.13091.

3. M.C. Taylor, T.L. Laber, P.E. Kish, G. Owens, N.K.P. Osborne, The

Reliability of Pattern Classification in Bloodstain Pattern Analysis - PART 2:

Bloodstain Patterns on Fabric Surfaces, J. Forensic Sci. 61 (2016) 1461–1466.

https://doi.org/10.1111/1556-4029.13191.

2. Human Factors: All forensic science methods rely on human performance in acquiring,

examining, reporting, and testifying to the results. In the examination phase, some standards

rely heavily on human judgment, whereas others rely more on properly maintained and

calibrated instruments and statistical analysis of data.

2.1. Consensus View

The STRP believes this proposed standard effectively addresses issues pertaining
to human factors. This standard properly incorporateslinear sequential

unmasking – expanded (LSU-E) in an attempt to minimize the effects of

cognitive bias. The STRP believes LSU-E should be mentioned and discussed in

the Scope section of this standard and should be defined in the Terms and

Definitions section.

2.2. Minority View – None.

3. Quality Assurance: Quality assurance covers a broad range of topics. For example, a

method must include quality assurance procedures to ensure that sufficiently similar results

will be obtained when the methodology is properly followed by different users in different

facilities.

3.1. Consensus View

The STRP recognizes that this proposed standard is not a specific procedure or

method in bloodstain pattern analysis, but rather a methodological framework by

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which the bloodstain pattern analysis is supported. As such, traditional quality

assurance procedures would not be included. However, the STRP notes that the

proposed standard does include measures that guide the analyst toward a quality

work product if the methodology is employed properly.

3.2. Minority View – None.

4. Scope and Purpose: Standards should have a short statement of their scope and purpose.

They should list the topics that they address and the related topics that they do not address.

Requirements, recommendations, or statements of what is permitted or prohibited do not

belong in this section.

4.1 Consensus View (6/9)

The STRP believes there is room to clarify the scope as it pertains to the use of the

term “methodology”. The STRP recommends clarifying the distinction between

‘methodology’ from ‘methods’ in the scope section. Referencing examples of

methods that are not included in this document, e.g., a bloodstain pattern

classification method, may help clarify that the scope does not include technical

details of these methods. Consideration should be given to changing the title to

more clearly align the scope and purpose.

4.2 Minority Views

View 1 (3/9)

One, the term “methodology” is ambiguous, it is not explicitly recommended by

OSAC, and it may induce a reader to believe that the proposed standard describes

many of the principles and procedures required in BPA that the standard does not

address. The STRP therefore recommends “methodological framework in

bloodstain pattern analysis.” (The STRP recommends the same change in the
standard’s title.)

Two, and relatedly, the standard is intended to delineate best practices in

methodological framework—particularly in the sequencing of materials

considered by a blood trace analyst—in order to minimize the effects of cognitive

bias; the standard implements what has been termed “linear sequential

unmasking–expanded.” The STRP recommends that this be on the forefront in

the standard’s articulated Scope. The STRP also recommends explicitly

summarizing the concept of “linear sequential unmasking–expanded” in a

manner understandable to a layperson, legal scholar, or other ultimate user of the

proposed standard. A suitable definition might be that found on page 3 of source

[1]: “Always begin with the actual data/evidence—and only that data/evidence—

before considering any other contextual information, be it explicit or implicit,

reference materials, or any other contextual or meta-information.”

Three, again relatedly, the STRP recommends removing Section 5.6 of the

standard because it goes beyond the above-described scope.

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[1] I. E. Dror and J. Kukucka, "Linear Sequential Unmasking-Expanded

(LSU-E): A general approach for improving decision making as well as

minimizing noise and bias," Forensic Sci Int Synerg, vol. 3, p. 100161, 2021.

View 2 (5/9)

The STRP recommends removing the content in Section 5.6.1 of the proposed

standard because it goes beyond the above-described scope. The content of 5.6.2

should remain in the proposed standard.

4.3 Additional Comments Received After Voting

The problem with calling this document a "standard for methodology" is that

readers will think it specifies in detail how BPA should be performed--i.e., that it

provides a "standard method." But this document does not set forth a "standard

method." According to the Instructions for STRPs, a standard method must be

"sufficiently complete, standardized, and capable of producing repeatable,

reproducible, and accurate results for the uses described in the standard."

Furthermore, "[t]here must be sufficient evidence of the reliability of the method

or procedure—that it produces consistent results across instruments, examiners

and laboratories when used to analyze items like those encountered in casework."

This document meets neither of those requirements, hence it is misleading to

imply that it is a "standard method" for BPA.

Although it is not a "standard method", this is nevertheless a valuable document

because it sets forth thoughtful guidelines on steps that analysts can take to
reduce the potential for bias and improve the reliability of BPA. The suggestions

in this document primarily relate to the sequence in which various analytic steps

should be performed, without specifying how those steps should be performed.

Laying out this sequence of steps will be helpful in guiding professional practice.

It may also provide guidance for the eventual development of a true "standard

method" for the field. This document should have a title that describes what it

actually does, as the current title claims too much.

An STRP member thinks the subcommittee needs to exercise caution in making

this a “linear sequential unmasking” document. While steps have been

incorporated to address contextual bias through said unmasking, it is not what this

document is about. Furthermore, the STRP member cautions the use of the

suggested definition of “linear sequential unmasking” as considering only

data/evidence before considering other contextual information. While this

unmasking can be more easily achieved when performing an examination

remotely through photographs alone, it is virtually impossible when attending a

crime scene in person. Bloodstain pattern analysts work in context...they have

to...and at a crime scene, in particular, there may be contextual information that

is unavoidable. Follow-up bias safeguards are put in place during the technical

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review process of the written report where the reviewer is limited to the

information necessary for the BPA and can truly sequentially unmask during the

review process. (This is addressed in a separate OSAC document on Technical

Review).

5. Terminology: Standards should define terms that have specialized meanings. Only rarely

should they give a highly restricted or specialized meaning to a term in common use among

the general public.

5.1 Consensus View (7/9)

The STRP also recommends explicitly summarizing the concept of “linear

sequential unmasking–expanded” in a manner understandable to a layperson,

legal scholar, or other ultimate user of the proposed standard. A suitable

definition might be that found on page 3 of source [1]: “Always begin with the

actual data/evidence—and only that data/evidence—before considering any

other contextual information, be it explicit or implicit, reference materials, or

any other contextual or meta-information.” See also 4.2 View 1 end of paragraph

2.

[1] I. E. Dror and J. Kukucka, "Linear Sequential Unmasking-Expanded

(LSU-E): A general approach for improving decision making as well as

minimizing noise and bias," Forensic Sci Int Synerg, vol. 3, p. 100161, 2021.

5.2 Minority Views
View 1 (4/9)

The STRP recommends defining “methodology” to assist the reader in

understanding the difference between “methodology” and “method”.

View 2 (5/9)

Give consideration to contextual information only when it is task-relevant [one

member suggested to add this sentence to the end LSU-E’s definition provided in

the Consensus View].

5.3 Additional Comments Received After Voting

An STRP member believes that this standard should use the definition of

“cognitive bias” that was unanimously recommended by the Human Factors Task

Group. This definition is as follows:

"Cognitive bias – The class of effects by which an individual’s preexisting beliefs,

expectations, motives, and situational context may influence their collection,

perception, or interpretation of information, or their resulting judgments,

decisions, or confidence."

The source of the proposed language is Spellman, B.; Eldridge, H.; Bieber, P.

“Challenges to reasoning in forensic science decisions.” Forensic Sci

International: Synergy 2022 (in press,

https://doi.org/10.1016/j.fsisyn.2021.100200). The revised

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definition has been accepted for inclusion in ASTM E30 (WK77530) Standard

Practice for Core Forensic Responsibilities Training.

6. Method Description: There is no rule as to the necessary level of detail in the description of

the method. Some parts of the method may be performed in alternative ways without

affecting the quality and consistency of the results. Standards should focus on standardizing

steps that must be performed consistently across organizations to ensure equivalent results.

Alternatively, standards can define specific performance criteria that are required to be

demonstrated and met rather than specifying the exact way a task must be done. For example,

it may be enough to specify the lower limit for detecting a substance without specifying the

equipment or method for achieving this limit of detection.

6.1. Consensus View

The STRP considers that the proposed standard meets the Method Description

requirement. This opinion is based on the standard clearly defining six overall

standardized and chronologically ordered steps to perform a bloodstain pattern

analysis. Each of these six steps also include sub-steps and additional

information that provide detailed direction to provide the development of

interpretations supported by data from the analysis. Examples are provided
throughout the steps, which help reduce ambiguity and guide the reader. The

content and order of the proposed standard methodology to limit task-irrelevant

information (e.g., Requirements, Section 5.0, specifically including Section 5.4)

and the content pertaining to considering alternate hypotheses (e.g., Sections 5.5

and 5.6.2) are critically important for the standardization of BPA and

minimizing bias.

6.2. Minority View – None.

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7. Reporting Results: Methods must not only be well described, scientifically sound, and

comprehensive but also lead to reported results that are within the scope of the standard,

appropriately caveated, and not overreaching.

7.1. Consensus View (6/9)

7.2 Minority View 1 would be acceptable if the whole section 5.6.1 is removed

while the content of 5.6.2 remains. [See also Consensus View 6.1 “5.6.2” is

“critically important”]

7.2. Minority Views

View 1 (3/9)

Reporting results is outside the scope of this document, therefore not applicable.

View 2 (1/9)

Minority View 1 would be acceptable if the whole section 5.6 is removed. [See

also 4.2 Minority View 1 “the STRP recommends removing Section 5.6 of the

standard because it goes beyond the above-described scope”]

7.3. Additional Comments Received After Voting
An STRP member recommends removing any reference to the Report Writing

Document in 5.6.2 (e.g., Referred to as the Case Conclusion Section of the

Report Writing Document). An STRP member is uncertain that it does refer to

that section of the Report Writing document. Furthermore, if that document

should ever change its wording in the future, it would require a change to this

document.

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