1. Strategies eyewitnesses use in lineup identification decisions
Colin Tredoux
Alicia Nortje
Kate Kempen
University of Cape Town
South Africa
Jacques Py
Céline Launay
Romain Bouvet
Université de Toulouse
France
AP-LS Conference  San Diego  March 2015

2. Acknowledgements
The team The funders

3. Summary
Is it possible to use self-reported decision processes to evaluate the accuracy of an eyewitness identification? c.f. Dunning and Stern (1994)
We report
an interview method we used to recover types of decision process in eyewitnesses
a self-report questionnaire, based on a)
an empirical study that uses b) to evaluate and predict accuracy of eyewitnesses to a simulated crime

4. To a considerable extent, eyewitness identifications are inscrutable
[Identification evidence] ... is exceptionally difficult to assess. It is impervious to the usual tests. The two ways of testing a witness are by the nature of his story – is it probable and coherent? – and by his demeanour – does he appear to be honest and reliable? [In] identification evidence there is no story; the issue rests on a single piece of observation. The state of the light, the point of observation, and the distance from the object are useful if they can show that the witness must be using his imagination. But otherwise, where there is a credible and confident assertion, they are of little use in evaluating it (Judge Patrick Devlin, in Shepherd, Ellis, & Davies, 1982, p xx).

5. Correlates of eyewitness accuracy
Most enduring
Some other candidates
Confidence at the time of the identification (many studies, see Brewer, 2006, for a review)
How quickly the identification is made (Sporer, 1992, & others)
Ability to identify lineup foils
Accuracy of initial description
Degree of absolute vs relative judgement
If witness chooses someone
Degree of attention paid during event
It would be bad advice to suggest a halt to estimator-variable research. However, in undertaking an applied project, it is incumbent on a researcher to demonstrate the applied utility of an eyewitness study (Wells, 1978, p 1555)

6. Our study program
Part 1 Interviews with 34 witnesses (to a simulated theft from a bookshop), during and after lineup identifications Part 2 Analysis of interview transcripts to identify decision processes, and to express these as questionnaire items Part 3 Testing of questionnaire, including empirical study of 117 eyewitnesses (still under way)

7. Part 1 – Interviews
Eyewitness views video depicting theft from bookstore
… makes identification from photo lineup (this is filmed)
… explains why they made their choice
… views the film of themselves making their identification
… explains again why they made their identification
… is then given photo lineup again, asked to view the film again, and asked to explain again why they made their identification

9. Part 2 - Questionnaire
17 items were constructed from the transcript analysis Exploratory Factor Analysis of responses by 117 eyewitnesses provided strong evidence for three factors
Factor 1 “Evoked recognition response” (popout?!)
I immediately recognized the person, he stood out from the others
Factor 2 “Elimination strategy”
I first eliminated the ones definitely not him, then chose among the rest
Factor 3 “Conservative strategy”
I did not get a good look at the perpetrator’s face, so I could not recognise it later

10. Part 3 – evaluating witnesses
117 students saw a simulated crime, attempted a lineup identification, and then completed the questionnaire (+ confidence, + latency)
(also, some sampling factors: two targets, two lineup orders, all counterbalanced)

11. Part 3 – analysis and results
How do the decision strategies relate to confidence and reaction time?

12. Part 3 – analysis and results
Are the decision strategies predictive, over and above what can be gleaned from confidence and RT?
Do the decision strategies predict accuracy?
To answer both of these sets of questions we conducted a logistic regression, modeling lineup accuracy (dichotomy) with the decision strategies, and the design variables

13. Part 3 – analysis and results
Are the decision strategies predictive, over and above what can be gleaned from confidence and RT? YES

14. Part 3 – analysis and results
2. Do the decision strategies predict accuracy? (especially when combined with the design variables) YES

15. Part 3 – analysis and results
Predictive accuracy of model (confusion matrix) To assess overfitting, package Caret in R was used with 6 fold cross validation – this produced an average error rate of 86% across the folds , with 95% CI = (72% - 98%)

16. Part 3 – analysis and results
Predictive accuracy of model (confusion matrix) We used design variables in our model, but in a particular case, we would not know whether a lineup is TP or TA. It is possible to measure lineup bias and lineup size, though, and it seems possible to us to estimate encoding opportunity If we drop the design variables our prediction accuracy = 70%, and if we add in the confidence and latency variables accuracy = 75%

17. Part 3 – analysis and results
The logistic regression modeling suggests a predictive and complex pattern Some speculation: Positive evoked recognition decisions are very predictive, especially in target present lineups Elimination strategies are associated with poor decisions, especially in target absent lineups Conservative strategies are associated with good decisions, especially for poor quality lineups

18. Conclusion
Eyewitness decision strategies are reportable, and predictive
replicates Dunning & Stern (1994), and others (e.g. Bellinger & Lindsay, 1999; Kneller et al., 2001, and still other studies), but inductively rather than deductively.
Assessing these strategies in a fairly simple way leads to fairly high levels of predictive accuracy
BUT we need to replicate this finding in multiple ways: different crime simulations, different populations
We are currently adding some other predictors : strategies in relation to each of the lineup members, not just globally