Putting bias into context: The role of familiarity in identification.

Previous demonstrations of context effects in the forensic comparison sciences have shown that the number of "match" responses a person makes can be swayed by case information. Less clear is whether these effects are a result of changes in accuracy (e.g., discrimination ability), a shift in response bias (e.g., tendency to say "match" or "no match") or a mix of the 2. We present a series of experiments where we use a signal detection framework to examine the effects of case information (separately) on forensic comparison accuracy and response bias. We also explore the role of familiarity as 1 potential mechanism for case information to sway accuracy. In Experiment 1, case information about crimes perceived to be more severe swayed people to say "match" more, but had little bearing on their ability to discriminate matching and nonmatching fingerprint pairs. In Experiment 2, case information did affect accuracy when it was familiar (i.e., if a previous similar case was associated with a "match" then people were more likely to also rate the current case as a "match," even though it was not). Even when we blinded people to all extrinsic case information in Experiment 3, accuracy was significantly affected by the familiarity of the fingerprints. These results demonstrate that contextual factors can have different (and independent) influences on accuracy and response bias and that even subtle information can affect accuracy if it is sufficiently similar to the case or trace at hand.