DOI: 10.3886/icpsr38947.v1
title: Testing a ''Not Sure'' Instruction as a Prophylactic Against the Harmful Impact of System and Estimator Variables on Lineup Identification Accuracy, United States and United Kingdom, 2019-2023
title: Version 1

description: Eyewitness lineup identification accuracy is affected by numerous variables, including those that are under the control of the legal system, called system variables (e.g., pre-lineup instructions), and those that are not under the control of the legal system, called estimator variables (e.g., the race of the perpetrator). One of the ultimate goals of eyewitness researchers is to develop procedures that:

minimize false identifications caused by system and estimator variables (while minimizing any decrease in correct identifications), and require few resources for law enforcement to enact.


The project tested the effectiveness of a system variable--providing witnesses with an explicit 'not sure' instruction before viewing the lineup-- that potentially meets both of these criteria. Furthermore, a 'not sure' instruction may act as a prophylactic against the harmful effects of system and estimator variables known to inflate false identifications. The specific objective of the research was to test the effectiveness of this 'not sure' instruction.
description: <strong>Pilot study</strong>

The pilot study conformed to a 2 (target status: target-present vs. target-absent) X 3 (instruction: 'don't know' vs. 'not sure' vs. none) X 2 (pre-lineup instruction regarding response option: given vs. not given) between-subjects design. Participants were randomly assigned to all conditions. Participants (undergraduate students: n = 322) viewed one of four mock crimes (carjacking, store theft, graffiti, or bike theft), were either given a pre-lineup instruction regarding the withholding response option that would be presented to them or not, viewed a target-present or target-absent lineup, were either presented with an option to withhold their decision ('not sure,' don't know,') or not, and made an identification decision and provided their confidence.




<strong>Study 1</strong>

Study 1 conformed to a 2 (target status: target-present vs. target-absent) X 2 (response option: 'not sure' vs. none) X 2 (appearance-change instruction: present vs. absent) between-subjects design. Participants were randomly assigned to all conditions. Participants (recruited online via Prime Panels: n = 2137) viewed one of four mock crimes (carjacking, store theft, graffiti, or bike theft), were either given the Appearance Change Instruction (ACI) or not, were presented with either a target-present or target-absent lineup, were either given the option of responding 'not sure' (accompanied by a corresponding pre-lineup instruction) or not, and made an identification decision and provided their confidence.




<strong>Study 2</strong>

Study 2 conformed to a 2 (target status: target-present vs. target-absent) X 2 (response option: 'not sure' vs. none) X 2 (perpetrator race: cross-race or same-race) between-subjects design. Participants were randomly assigned to all conditions.
Participants (Black and White, recruited online via Prolific: n = 2097) viewed one of four mock crimes (all of which depicted a man stealing a laptop from a woman) in which they viewed either a same-race perpetrator or a cross-race perpetrator, were presented with either a target-present or target-absent lineup, were either given the option of responding 'not sure' (accompanied by a pre-lineup instruction) or not, and made an identification decision and provided their confidence.
description: Three quantitative data sets were generated, and the datasets can be linked together with the unique ids; <strong>PARTICIPANTID</strong> and <strong>PARTICIPANTNUMBER</strong>. Pilot Study Data includes the participants confidence in their identification decision, how likely was the the suspect the participants picked guilty, the strength of the participants memory of the perpetrator's face, and the condition the participants was in. Study 1 Data topic area includes the mock crime participants saw, if they received the appearance change instruction (ACI) or not, and if they received a clear image of the perpetrator. Study 2 Data describes race of the participants and the "mock" crimes (carjacking, store theft, graffiti, or bike theft) the participants "witnessed". 
 Also, in Study 1, 12% responded 'not sure' among participants who received the 'not sure' option, and in Study 2, 19.3% responded 'not sure' among participants who were given the 'not sure' option.
description: Presence of Common Scales: Several Likert-type scales were used.
description: Datasets: 
DS0: Study-Level Files
DS1: Pilot Study Data
DS2: Study 1 Data
DS3: Study 2 Data
description: Pilot and Study 1: US English-speaking adults of all races.
Study 2: Black and White English-speaking adults from the US and the UK.
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description: web-based survey