Ryan Ditchfield_Confirmation Bias in the Manipulation of Police Lineups

Running Head: CONFIRMATION BIAS IN POLICE LINEUPS 1

Confirmation Bias in the Manipulation of Police Lineups

Ryan Ditchfield

California State University, Fresno

CONFIRMATION BIAS IN POLICE LINEUPS 2

Abstract

Several factors contribute to inaccurate eyewitness identifications of suspects in photo

lineups. One recommendation to increase their accuracy is to present the lineup using a double-

blind procedure. Here, the administrator of the lineup does not know the identity of the suspect

and is thus protected against confirmation bias (i.e., the tendency to only seek out information in

support of some belief). Photo lineups typically consist of six photographs – one of the suspect

and five non-suspects (fillers). All of the photographs must be similar to one another but not so

similar that the photographs are indistinguishable. Photographs that are too similar make

identification difficult; dissimilar photographs make identification too easy. In some cases,

suspects possess a characteristic that distinguishes them from the fillers. The presence of this

feature may make identification too easy. It is recommended that the distinguishing feature be

either replicated across all photographs or concealed on the photograph of the suspect. In this

experiment, we examined the effects of confirmation bias on the concealment of a distinguishing

feature (hairstyle) on photographs in a lineup. We tested whether a participant’s knowledge of

the suspect caused them to conceal the distinguishing feature differently for the suspect’s image

versus the filler images. Half of the participants knew the identity of the suspect, forming the

experimental group; the other half did not, forming the control group.

The distinguishing feature in this experiment was the suspect’s hair. It was pulled back

into a ponytail, resulting in a hairstyle different than those of the fillers. Both groups were

instructed to give each of the individuals as similar a hairstyle as possible using a black felt-tip

marker. The surface area of the concealed images was measured using the image-processing

program ImageJ. Results show that participants who knew the identity of the suspect concealed

the distinguishing feature in the same manner as participants in the control group (p>0.05).


However, an analysis of the standard deviations of the lineups shows that participants who knew

the identity of the suspect concealed the hairstyles in a more inconsistent manner than

participants who did not know the suspect’s identity (p<0.05). Furthermore, participants who

knew the suspect’s identity concealed medium and large hairstyles more inconsistently than

participants in a double-blind setting. This suggests that, under certain conditions, knowledge of

a distinguishing feature may result in inconsistent concealment. Therefore, while the results of

the second pilot study do not support confirmation bias having a significant effect on the type of

concealment used, they do suggest that police lineups can benefit from a double-blind procedure.


Confirmation Bias in the Manipulation of Police Photo Lineups

Eyewitness identification is a powerfully persuasive tool in the criminal justice system.

From identifications during police lineups to identifications by witnesses in the courtroom,

eyewitnesses often form the crux of investigations and trials. In extreme cases, an eyewitness

may provide the only piece of evidence that persuades a jury to find a defendant guilty beyond a

reasonable doubt. Yet of the 311 individuals exonerated by DNA evidence in the United States,

73% were convicted as a result of inaccurate eyewitness identification (Innocence Project, 2014).

This is not to suggest that eyewitnesses are inherently dishonest. Decades of research have

shown that even confident and honest witnesses can be fallible. This study focuses on the

possible effects of confirmation bias on the concealment of identifying facial characteristics in

police photo lineups. Confirmation bias is defined here as the intentional or unintentional

communication of information that might influence a witness to select the individual who the

police believe committed the crime. It has been well established that human memory does not

record sensory information like a video camera. Rather, memory is a reconstructive process

where, for example, information presented after an individual witnesses an event can change

how that person later recalls the event, and can even produce false memories (Loftus, 2005).

Therefore, confirmation bias may cause a witness to make a false-positive identification (i.e.,

incorrectly identify an innocent person as the perpetrator) by providing misleading post-event

information.

This study will examine the effects of confirmation bias on the manipulation of police

lineups, in the absence of double-blind procedures. Thus, the hypothesis in the current study is

that participants who know the identity of a suspect in a photo lineup and are instructed to

conceal an identifying facial characteristic will do so differently than participants who are given


the same task but do not know the suspect’s identity. While the presence of confirmation bias in

the manipulation of lineups may not necessarily lead to eyewitness misidentification, it may still

produce lineup bias and lead to reduced similarity of concealment among lineup members.

Reduced similarity may lead to increased suggestibility in the lineup. To illustrate this point

using an extreme example: a lineup in the 1967 Supreme Court case United States v. Wade

consisted of five men over 40 years of age and one teenage suspect (Wogalter, Marwitz, &

Leonard, 1992). However, even in well-designed lineups, reduced similarity following

manipulation may lead to a higher rate of false-positive identification by witnesses. Therefore,

this research will be important in informing police agencies of a potential risk in the

manipulation and administration of photo lineups.

Background and Definitions

A police photo lineup is a procedure in which a photograph of a criminal suspect and

non-suspects (called fillers) are presented to a witness in the hope that the witness can positively

identify the culprit (Wells & Olson, 2003). Fillers in this context are individuals who resemble

the description of the perpetrator (Innocence Project, 2014), and exist to lower the rate of false

positive identifications by witnesses. Photo lineups typically consist of six photographs – one of

the suspect and five non-suspects (fillers). All of the photographs must be similar to one another

but not so similar that the photographs are indistinguishable. Photographs that are too similar

make identification difficult; dissimilar photographs make identification too easy. In some cases,

suspects may possess a characteristic that distinguishes them from the fillers (i.e., a scar or

tattoo). The presence of this feature may make identification too easy, opening the door to false-

positive errors by witnesses. The Technical Working Group for Eyewitness Evidence, a

committee created by the Department of Justice, addresses lineups in its Eyewitness Evidence


Trainer’s Manual for Law Enforcement (2003). The Department of Justice recommends that

investigators compose photo lineups “in such a manner that the suspect does not unduly stand

out” (Technical Working Group for Eyewitness Evidence, 2003, p. 39). To do so, investigators

must include a minimum of five fillers per lineup and create a consistent appearance between the

suspect and fillers with respect to any unique or unusual features.

Police departments currently use two types of manipulation techniques to create

consistent appearances among photographs that may possess unique or unusual features:

replication and concealment. Under replication, unique or distracting features present in the

suspect are replicated across the fillers. For example, imagine a lineup where the suspect

possesses a tattoo on her left cheek. In this instance the investigator would replicate the tattoo

onto the left cheek of all filler photographs to create a consistent appearance. In contrast,

concealment involves eliminating or covering up the unique characteristic. Concealment and

replication can be accomplished through either photo-editing software (e.g., Adobe Photoshop)

or physical manipulation, such as obscuring and replicating details on the photographs using a

permanent marker. The Department of Justice does not recommend one method over the other –

the recommendations in the Trainer’s Manual serve only as a guide for law enforcement.

Consequently, there remains no regulation or suggestion on preference between the two

techniques, and no regulation on how to use the techniques. This means that implementation of

replication and concealment varies widely across jurisdictions (Wogalter, Malpass, &

McQuiston, 2004).

Dr. Gary L. Wells, a leading cognitive psychologist in the field of eyewitness

identification, defines lineup bias as “characteristics of the lineup that make an innocent suspect

stand out in ways that could increase the chances that the suspect is identified” (Wells &


Bradfield, 1999, pp. 527-528). In simultaneous lineups—lineups where fillers and the suspect are

shown at the same time rather than sequentially (i.e., one at a time)—eyewitnesses tend to use a

relative judgement strategy. That is, the selection of the “perpetrator” may be based on who

among those present in the lineup most matches the witness’s memory of the suspect (Zarkadi,

Wade, & Stewart, 2009). In this way, eyewitnesses may make false-positive identifications—

even if the selected “suspect” is not the actual perpetrator. Several factors contribute to

inaccurate eyewitness identifications of suspects in photo lineups. Estimator variables lie outside

the criminal justice system and can include own race bias or visibility at the scene of the crime.

System variables, on the other hand, refer to those factors that the criminal justice system can

influence or control (Wilford & Wells, 2013). The implementation of lineups falls under the

latter category. Notably, these factors often mirror confounding variables present in social

science experiments. As Wells notes, “all the types of things that can go wrong with an

experiment to cause misleading results can also go wrong with a lineup (Wells & Olson, 2003, p.

528)”. Fortunately, this similarity means that potential flaws in lineups can be examined both

qualitatively and quantitatively in an experimental setting.

The theory driving this study is confirmation bias, defined here as “the seeking or

interpreting of evidence in ways that are partial to existing beliefs, expectations, or a hypothesis

in hand” (Nickerson, 1998). Confirmation bias presents several problems for the criminal justice

system generally and the implementation of lineups specifically. For example, an officer who

purposely persuades a witness to identify a particular suspect has undoubtedly violated the

suspect’s right to due process. Yet an officer who does so unknowingly may have the same

effect, despite lacking some nefarious intent. Officers can influence the accuracy of an

eyewitness’s recollections (i.e., retrospective certainty) by providing feedback that bolsters the


witness’s confidence in his or her recollection (Bradfield, Wells, & Olson, 2002). The Technical

Working Group for Eyewitness Evidence advises law enforcement to perform double-blind

administration of lineups in order to avoid confirmation bias on behalf of the investigator

(Technical Working Group for Eyewitness Evidence, 2003). However, many jurisdictions

remain resistant to double-blind administration. Even in New Jersey, the first jurisdiction to

adopt this policy, only 77% of police departments reported using double blind administration in

every case (Rodriguez & Berry, 2013). Furthermore, the question of whether double-blind

administration should extend to the individual conducting replication or concealment of the

lineup appears to remain unanswered by current research. Therefore, inquiry into this area is

necessary to inform law enforcement agencies of potential risks and biases that may otherwise be

unknown to them.

One recommendation to counteract the possible presence of confirmation bias on police

photo lineups is to present the lineup using a double-blind procedure (Technical Working Group

for Eyewitness Evidence, 2003). In this procedure, the administrator of the lineup does not know

the identity of the suspect and is therefore precluded from communicating any potentially biasing

information to the witness. However, there is currently no body of research that examines

whether the need for a double-blind procedure extends to the manipulation of lineups. The

proposed research aims to improve current understanding of the two manipulation techniques

(concealment and replication), and to identify the potential strengths and weaknesses of each.

This study will examine whether individuals who use concealment are subject to confirmation

bias. In addition, this study examines the consistency of concealment and replication under

double-blind and non-blind settings to address the Department of Justice’s requirement of


similarity among lineup members. Finally, this research will recommend to law enforcement

appropriate techniques in implementing effective, bias-free line ups.

Methods

This study will use a sample of 118 undergraduates from California State University,

Fresno. Participants will be recruited from upper-division courses within the Department of

Criminology. Upon arrival, the general nature of the research will be described and informed

consent will be obtained. Extra credit points will be rewarded for participating; students who do

not wish to participate in the study will be provided with an alternative activity in order to obtain

the extra credit. Participants will be randomly assigned to either the experimental or control

groups, and will be provided with the written instructions appropriate for their respective group.

All participants will be instructed on the purpose of lineups and the investigative intent for either

concealing or replicating a suspect’s distinguishing features. Furthermore, all participants will be

instructed to assume the role of the investigator whose job it will be to use the permanent

markers to replicate the distinguishing feature as consistently as possible on all photos contained

in the lineup. Both groups will be given copies of the same photo lineup, consisting of one

suspect and five fillers. Images for use in the photo arrays will be compiled from online public-

record sources of suspect’s booking photographs. Participants will be provided with permanent

black-felt tip markers with which they are to perform the replication task. At this point,

participants will be asked to complete reading of the instructions on their own. Instructions for

the experimental group will reveal the identity of the suspect. The suspect will not be identified

for the control group.

The task given for both groups is as follows: participants must consistently conceal a

unique hairstyle in the given lineup, using a black felt-tip marker. The suspect in the lineup has a


pony tail, and all the fillers have short hair. While the experimental group is aware of this

difference, the control group is not. In other words, the control group will mimic the conditions

of an investigator under double-blind conditions. When they have completed reading the

instructions, participants will have 15 minutes to complete the task. Participants will be debriefed

as to the nature of the experiment, thanked and dismissed. The surface area of the concealment

for both the control and experimental groups will be measured in pixels using the image-

processing program ImageJ. Due to difference in face size among lineup members, a correction

factor will be calculated using the following formula:

Xxn

=Correction Factor .

Where X is mean facial surface area for the entire untouched lineup, and xn is the facial surface

area of the original untouched lineup member. Lineup members are then multiplied by the

correction factor to produce a surface area that accounts for differences in face size.

Analysis of the concealment consists of two parts: a quantitative analysis of the method

of concealment and a quantitative analysis of the consistency of concealment. The method of

concealment is determined by comparing the mean concealed surface area of the experimental

and control groups. Consistency is determined in two ways. First, it will be determined by

comparing the average standard deviations between the two groups. Second, it will be

determined by an independent comparison of each lineup member when compared to that

lineup’s mean concealed surface area. This study will employ a two-sample t-test assuming

unequal variances when comparing means and standard deviations between the control and

experimental group. The consistency criteria for the independent comparison of lineup members

will show the rate of inconsistencies within individual lineups and between the experimental and

control groups. It will be determined using the following formula:


( SCx+SEx

2 )×0.75=Consistency Criteria for Group .

Where S is average standard deviation, C is control group, and E is experimental group. The

equation is multiplied by 0.75 to produce an “ideal” consistency criterion that accounts for the

high burden of proof in criminal court. Note that this number is only temporary and used for the

purposes of this preliminary pilot study; future research in this area will need to provide a

number substantiated by outside research. X is lineup group size as determined by the table

below, which includes calculated consistency criteria for each group size.

Using this criteria, each lineup member’s concealed surface area is compared against the mean

concealed surface area for the entire lineup. It is then marked “consistent” if the difference

between the lineup member and the lineup mean is less than or equal to the consistency criteria,

as denoted by the following formula:

|X−xn|≤Cg .

Where X is the mean of the concealed surface area for the lineup, xn is the concealed surface

area for the individual lineup member, and Cg is the consistency criteria for the lineup, as

determined by lineup’s group size. If it does not meet this standard, the lineup member is marked

as “inconsistent.”

Group size name: Mean concealed surface area of lineup: Consistency Criteria:

Small Size <48.000 pixels Within 4,200 pixels of mean for lineup

Medium Size 48,000-66,000 pixels Within 5,500 pixels of mean for lineup

Large Size >66,000 pixels Within 5,800 pixels of mean for lineup


Preliminary Results

In the first of two pilot experiments, the effects of confirmation bias on the concealment

of a distinguishing feature on photographs in a lineup were examined. The experimental and

control groups were each comprised of twenty college undergraduates. The study tested whether

a participant’s knowledge of the suspect caused them to conceal the distinguishing feature

differently for the suspect’s image versus the filler images. Participants in the experimental

group knew the identity of the suspect; participants in the control condition did not. Both groups

were instructed to conceal the photographs in as similar a manner as possible using a black felt-

tip marker. The surface area of the concealed images was measured using the image-processing

program ImageJ. After correcting for image size and pixel count, the mean concealed surface

area for all participants was calculated. The average concealed surface area for the experimental

group was 68100 pixels. The average concealed surface area for the control group was 46800

pixels. This supports the hypothesis that knowledge of a suspect’s identity may cause an

individual to conceal a distinguishing feature differently on a suspect than on a non-suspect

(p<0.05), thus supporting the apparent presence of confirmation bias.

Analysis of Results for Current Study

This paper uses the results of a second pilot experiment, which addresses several of the

limitations and assumptions present in the first pilot experiment. It uses a larger sample size

(approximately three times larger), accounts for differences in shading between photos, and

improves the picture quality. It also includes an analysis of consistency within lineups, in

addition to the comparison between lineups. However, it does not address the other assumptions

and limitations present in the first pilot, and does not include subjective measures of consistency,

concealment, and obstructiveness. The analysis of results will take place in two parts. First, mean


concealed surface area for the lineups is compared using a two-tailed t-test of independent

means, in order to determine the presence of confirmation bias. Second, similarity of

concealment is examined through a comparison of standard deviations of concealment within

lineups (using a two-tailed t-test) and an analysis of inconsistencies within lineups using the

previously described consistency criteria.

Mean Concealed Surface Area and Confirmation Bias Analysis

As shown in Figure 1 below, the mean concealed surface area for the control group was

58126 pixels with an average standard deviation of 6411 pixels among lineup members, whereas

the mean concealed surface area for the experimental group was 58511 pixels with an average

standard deviation of 7764 pixels among lineup members.

Unlike the first pilot, there was no statistically significant difference in the mean

concealed surface area between the experimental and control groups in the second pilot

experiment (p=0.892). The second pilot therefore fails to support the presence of confirmation

Figure 1 (above) shows the distribution of mean concealed surface areas for the control and experimental groups. The method of concealment, in terms of surface area, was right-skewed. Most participants concealed within the 42,000-72,000 pixel range. However, the method of concealment in the experimental group was more concentrated in the medium spectrum (48,000-66,000 pixels).

24000-30000

30000-36000

36000-42000

42000-48000

48000-54000

54000-60000

60000-66000

66000-72000

72000-78000

78000-84000

84000-90000

90000-96000

96000-102000

108000-114000

114000-120000

138000-1440000

2

4

6

8

10

12

14

16

Mean Concealed Surface Area for Lineups

Experimental Control


bias in the manipulation of police lineups, since there was no significant difference in how the

two groups of participants concealed the lineups. It is worth noting, however, that most

participants, regardless of knowledge, chose to conceal the lineups using a hairstyle that fell

within the medium spectrum (48,000-66,000 pixels). This does not necessarily mean that this is

the most effective method of concealment; it simply shows that under current instructions

participants have a tendency towards using this method. Future qualitative analysis may be

necessary to determine the subjective effectiveness of different concealment methods.

Consistency and Similarity Analysis

Although a comparison of mean concealed surface areas does not support the presence of

confirmation bias in lineup manipulation, knowledge of the suspect still appears to have an effect

on the consistency of concealment. The graph below (Figure 2) shows that concealment of

control group lineups was more consistent—with a lower average standard deviation—than the

experimental group (p=0.023).

Figure 2 (on right) shows the distribution of standard deviations (in pixels) among lineup members. Participants who did not know the suspect’s identity concealed the lineups in a more similar manner, on average, than participants who knew the suspect’s identity (p=0.023). 0-3000 3000-6000 6000-9000 9000-12000 12000-15000 15000-18000

0

5

10

15

20

25

30

Standard Deviations for Concealment within Lineups

Experimental Control


In other words, while knowledge

of the suspect did not affect the

overall method used to conceal,

it did affect the similarity of

concealment among lineup

members. Furthermore, the rate

of inconsistency varied

according to the method of

concealment used, and whether

the participant knew the identity

of the suspect. Participants that

chose to employ medium and

large hairstyles to conceal the

lineup were more inconsistent

when aware of the suspect’s identity, while participants that chose to employ small hairstyles had

the same rate of inconsistency regardless of knowledge.

The following frequency tables show the rate of inconsistencies in the control and

experimental groups. Consistency was calculated using the consistency criteria equation

described previously. Participants who knew the suspect’s identity were less consistent when

using medium and large hairstyles to conceal the lineup, and were less consistent overall

(43.79% inconsistent compared to 36.42% inconsistent for the control group). This suggests that

knowledge of the suspect did have an effect on similarity of concealment.

Table 1 (above-left) shows the rate of inconsistencies within lineups for the control group.

Table 2 (below-left) shows the rate of inconsistencies within lineups for the experimental group.

Participants that used a small

Control Group Consistency Analysis

Count of inconsistencies per lineup (IC) Small Medium Large

0 1 3 31 4 4 22 5 9 63 3 3 04 3 2 25 0 0 26 2 0 0

Total IC/Possible IC: 47/108 39/126 32/90Percent IC: 43.52% 30.95% 35.56%

Experimental Group Consistency Analysis

Count of inconsistencies per lineup (IC) Small Medium Large

0 0 5 01 0 2 22 6 6 43 3 15 34 0 6 35 1 3 06 0 0 0

Total IC/Possible IC: 26/60 98/222 31/72Percent IC: 43.33% 44.14% 43.06%


Assumptions and Limitations

Preliminary pilot experiments have demonstrated several limitations that will need to be

addressed in the future. First, the size of the heads in the photographs varied. The differences in

face proportions may have led participants to conceal the hairstyle in such a way that the

concealed surface area was greater on larger faces. This became apparent in the first pilot’s

preliminary data, with smaller faces having a smaller mean surface area and larger faces having a

larger mean surface area. To account for this, a correction factor was calculated for each lineup

photo based on the surface area proportions of the original untouched lineup. Second, the

presence of confirmation bias was tested only in physical manipulation of lineups. The presence

Table 1 (above-left) shows the rate of inconsistencies within lineups for the control group.

Table 2 (below-left) shows the rate of inconsistencies within lineups for the experimental group.

Participants that used a small


of confirmation bias in digital manipulation of lineups should also be tested. Third, the study

focused on no other unique identifying characteristics other than hairstyle. Fourth, this study

does not address the effects of confirmation bias on eyewitness identification, but rather on the

manipulation of lineups. It is possible that the presence of confirmation bias in the prior

manipulation of police lineups may have little or no effect on an eyewitness’s behavior during

identification. Fifth, the data in the first two pilot experiments was not measured using a double-

blind procedure, due to time constraints. This means that the analysis may be subject to

confirmation bias. Sixth, because the order of the photographs in the lineup was not randomized,

the data may be subject to a practice effect. Seventh, this paper only includes quantitative

analysis of the concealed surface areas for the photo lineups. Future drafts will also include a

qualitative analysis, in order to provide subjective measures of concealment, consistency, and

obstructiveness (i.e., concealment which covers up other identifying features and/or is

distracting) that cannot be addressed with current methods. This may take the form of a survey in

which the lineups concealed in the first stage of the experiment are presented to a new group of

participants. The new group will then rate the lineups based on three criteria: concealment,

consistency, and obstructiveness.

Finally, this study is subject to the same limitations as all social science “laboratory

setting” experiments, in that it is difficult to apply results obtained in a controlled experimental

setting to the real world. However, this study assumes that the results are applicable to law

enforcement, and that while this study may not mirror the same settings and pressures as exist in

actual police investigations, it still provides a useful framework for formulating future lineup

policy and procedures.

Discussion and Conclusion


The results of this study fail to support the presence of confirmation bias, but may still

serve as a useful guide for law enforcement officials. Based on the quantitative analysis of mean

surface area, it can be concluded that knowledge of a suspect’s identity does not affect the

method by which an investigator chooses to physically conceal a unique hairstyle in a police

lineup. However, knowledge of a suspect’s identity does produce a higher rate of inconsistency

when an investigator chooses to employ either medium or large hairstyle to conceal the

identifying feature in a lineup. Furthermore, knowledge of a suspect reduces similarity among

lineup members. It appears that the most consistent method of physically concealing a unique

hairstyle is to employ a medium hairstyle under a double-blind procedure.

Of course, this data does not tell the entire story. Additional qualitative analyses may

produce guidelines for law enforcement that are more relevant, by providing subjective measures

of consistency, obstructiveness, and concealment. It is also unclear why participants were more

consistent under a double-blind setting. One could easily assume that the additional instruction

given to the experimental group would lead to increased consistency. Instead, the experimental

group produced less similar lineups that were concealed with a higher rate of inconsistency. One

potential explanation is that participants in the control group were more careful in their

concealment. Another explanation is that the added instruction caused the experimental group to

“try harder” on certain lineup members, leading to a higher rate of inconsistency. Future studies

should employ a post-experiment survey to determine the reasons behind participants’ decisions.

References


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Ryan Ditchfield_Confirmation Bias in the Manipulation of Police Lineups