Author(s): Koehler JJ
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Abstract The way in which statistical DNA evidence is presented to legal decision makers can have a profound impact on the persuasiveness of that evidence. Evidence that is presented one way may convince most people that the suspect is almost certainly the source of DNA evidence recovered from a crime scene. However, when the evidence is presented another way, a sizable minority of people equally convinced that the suspect is almost certainly not the source of the evidence. Three experiments are presented within the context of a theory ("exemplar cueing theory") for when people will find statistical match evidence to be more and less persuasive. The theory holds that the perceived probative value of statistical match evidence depends on the cognitive availability of coincidental match exemplars. When legal decision makers find it hard to imagine others who might match by chance, the evidence will seem compelling. When match exemplars are readily available, the evidence will seem less compelling. Experiments 1 and 2 show that DNA match statistics that target the individual suspect and that are framed as probabilities (i.e., "The probability that the suspect would match the blood drops if he were not their source is 0.1\%") are more persuasive than mathematically equivalent presentations that target a broader reference group and that are framed as frequencies ("One in 1,000 people in Houston would also match the blood drops"). Experiment 3 shows that the observed effects are less likely to occur at extremely small incidence rates. Implications for the strategic use of presentation effects at trial are considered.
This article was published in Law Hum Behav
and referenced in Journal of Civil & Legal Sciences