Stephen J. Ross 1 , Roy S. Malpass 2 , & Lisa D. Topp 3 1 Florida International University

The importance of context and stimulus sampling in mockwitness

tasks:Perceptual similarity may not be enough

Stephen J. RossStephen J. Ross11, Roy S. Malpass, Roy S. Malpass22, & Lisa D. Topp, & Lisa D. Topp33

11Florida International UniversityFlorida International University22University of Texas at El PasoUniversity of Texas at El Paso

33Stephen F. Austin State UniversityStephen F. Austin State University

Evaluating Lineup Fairness

• Using Using mock witnessesmock witnesses– An individual who did not witness a crime but is asked to An individual who did not witness a crime but is asked to

view a lineup and select the suspectview a lineup and select the suspect

• RationaleRationale– If a lineup is constructed appropriately, each person in the If a lineup is constructed appropriately, each person in the

lineup should have an equal chance of being selectedlineup should have an equal chance of being selected

• Determining FairnessDetermining Fairness– Biased if proportion of suspect identifications differs from Biased if proportion of suspect identifications differs from

chance expectancychance expectancy – Lineup can also be considered unfair if the fillers in the Lineup can also be considered unfair if the fillers in the

lineup are not reasonable alternatives to the suspect lineup are not reasonable alternatives to the suspect

Lineup Fairness

• What is the MW task concerned with?What is the MW task concerned with?– Focus should be on having MW determine “who is the Focus should be on having MW determine “who is the

accused?” (Wells & Bradfield, 1998)accused?” (Wells & Bradfield, 1998)– ““Suspect stands out” or “Suspect stands out compared to Suspect stands out” or “Suspect stands out compared to

the the description of the perpdescription of the perp”?”?

• Similarity is associated with lineup fairness estimatesSimilarity is associated with lineup fairness estimates– Perceptual similarity is not just Perceptual similarity is not just physicalphysical similarity similarity

• Individuals also use inferred connotative information from Individuals also use inferred connotative information from individuals when forming similarity judgments (Rhodes, 1988; individuals when forming similarity judgments (Rhodes, 1988; Ross, 2008)Ross, 2008)

• MW report “criminality” as a contributor to choice (McQuiston & MW report “criminality” as a contributor to choice (McQuiston & Malpass, 2002)Malpass, 2002)

Three Questions….

• Does description presence influence lineup fairness?Does description presence influence lineup fairness?– Do MW use different information depending on presence Do MW use different information depending on presence

absence of description?absence of description?

• Does filler pool source influence MW evals?Does filler pool source influence MW evals?– Are college student filler pools equivalent to criminal filler Are college student filler pools equivalent to criminal filler

pools?pools?• Do they vary in similarity & inferred characteristics?Do they vary in similarity & inferred characteristics?• How does this variation influence lineup fairness assessments?How does this variation influence lineup fairness assessments?

• Does context influence lineup fairness?Does context influence lineup fairness?– Do MW use different information depending on the context Do MW use different information depending on the context

the photoarray is presented in (i.e., criminal v. volunteer)?the photoarray is presented in (i.e., criminal v. volunteer)?

Method - Materials

• Constructed 13 lineupsConstructed 13 lineups– 8 criminal8 criminal

– 5 layperson5 layperson

• Varied in similarityVaried in similarity

Very Dissimilar

Dissimilar

Moderately Similar

Very Similar

Very Dissimilar 1 --------- 2 --------- 3 --------- 4 --------- 5 Very Similar





Method – Participants & Procedure

• 689 undergrads689 undergrads– 129 trait/similarity raters129 trait/similarity raters– 560 mockwitnesses560 mockwitnesses

• Trait/Similarity ratingsTrait/Similarity ratings– Rated each individual on 7 characteristicsRated each individual on 7 characteristics– Assessed similarity of potential fillers with target Assessed similarity of potential fillers with target

individualindividual

• Mockwitness evaluationsMockwitness evaluations– Assessed lineup fairness (bias & size)Assessed lineup fairness (bias & size)

Results – Bias (desc)

Mock witness Bias estimate - Description Provided

0

0.1

0.2

0.3

0.4

0.5

0.6

1 - 100% dissimilar 1- maj. dissimilar 3 (v1) 3 (v2) 5 (v1) - mod similar 5 (v2) - mod similar 9 (v2) - very similar 9 (v3) - very similar

Lineup similarity version

Bia

s

Bias

Chanceexpectation

avg sim

r = -.81

Results – Size (desc)

Mock witness Lineup Size - Description Provided

0

1

2

3

4

5

6

7



Tre

do

ux

' E'

Tredoux E'

Nominalsize

avg sim

r = .64

Results – Bias (no desc)

Mock witness Bias estimate - No Description Provided

0

0.1

0.2

0.3

0.4

0.5

0.6



Bia

s

Bias

Chanceexpectation

avg sim

r = .21

Results – Size (no desc)

Mock witness Lineup Size - No Description Provided

0

1

2

3

4

5

6

7



Tre

do

ux

' E'

Tredoux E'

Nominalsize

avg sim

r = -.34

What are MW basing decision upon?

• When told suspected of committing a crime – Description provided: similarity # of MW choices – No description provided: criminality # of MW choices

Desc No desc

Choice/similarity .36 .14

Choice/criminality .17 .51

Do college students differ from criminals?

CriminalCollege Student

Similarity 2.7 2.9

Distinctiveness 4.8 4.7

Memorability 4.4 4.5

Attractiveness 1.6 2.6

Baby-facedness 2.2 3.1

Criminality 5.1 4.5

Dangerousness 4.8 4.5

Likeability 3.5 4.2

p = ns

p < .05

– College students produces lineups that are more unfair even though similarity is the same


Lineup Bias (College Students)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

1 2 3 4 5


Bias

Bias

Chanceexpectationavg sim

Lineup Bias (Criminals)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8



Bias

Bias

Chanceexpectationavg sim

– College students produces lineups that are more unfair even though similarity is the same


Lineup Size - Tredoux' E' (College Students)

0

1

2

3

4

5

6

7

1 2 3 4 5


Tred

oux'

E'

Tredoux E'

Nominalsize

avg sim

Lineup Size - Tredoux' E' (Criminals)

0

1

2

3

4

5

6

7



Tred

oux'

E'

Tredoux E'

Nominalsize

avg sim

Take-home Message

• Information used by MW varies as a function of description presence and question asked

• While college students did not differ from criminals in their perceived similarity to the target, they did differ on key inferred traits – Lineups using college students as fillers were evaluated to be more

unfair than lineups using criminal mugshots even though the perceived similarity was the same

• What is the appropriate question to be asked?Does the suspect stand out in the lineup?

OR

Taking into account the description provided by the witness, does the suspect stand out?

Current/Future Research

• Replication

• Similarity structure across various construction techniques

Thank You!!

• [email protected]

• http://www.fiu.edu/~ascl/

Documents

Stephen J. Ross 1 , Roy S. Malpass 2 , & Lisa D. Topp 3 1 Florida International University