Thinking About Low-Probability Events

Abstract

The way people respond to the chance that an unlikely event will occur depends on how the event is described. We propose that people attach more weight to unlikely events when they can easily generate or imagine examples in which the event has occurred or will occur than when they cannot. We tested this idea in two experiments with mock jurors using written murder scenarios. The results suggested that jurors attach more weight to the defendant's claim that an incriminating DNA match is merely coincidental when it is easy for them to imagine other individuals whose DNA would also match than when it is not easy for them to imagine such individuals. We manipulated the difficulty of imagining such examples by varying the description of the DNA-match statistic. Some of the variations that influenced the jurors were normatively irrelevant.

The Persuasive Powers of DNA: An Experimental Study in Perceptions of Expert Evidence

“…This study adopts an experimental approach via manipulations of case study information, specifically the format in which DNA evidence is presented, or not, to a sample of mock-jurors. The study replicates and extends the work of Koehler (2001) by utilizing a modified version of his case study of a fatal armed robbery (Koehler & Macchi, 2004). The study also takes up the findings from the Australian studies (Briody, 2003; in that the design includes a control group for which no specific DNA evidence is included in one of the case scenarios.…”

“…First, there are "single-targets" which focus on a specific individual or event, and "multi-targets" which focus on groupings of individuals or events (Koehler & Macchi, 2004). In addition there are two manipulations of the framing of the DNA statistic, either as a "probability" (expressed as 0.1%) or a "frequency" (expressed as 1 in 1,000).…”

“…It was once characterized in a It is, of course, difficult to argue against the power of DNA to incriminate the guilty, or deny its crucial role in exculpating the innocent, but like all powerful tools it has the capacity to produce undesirable consequences (Edmond, 2011; GoodmanDelahunty & Tait, 2006; Kirby, 2010;Langdon & Wilson, 2005;Lynch, 2013;McCartney, 2006). In the wake of the claim last century that little is known "about how laypersons respond to DNA evidence" (National Research Council, 1996), the body of research in this area has expanded significantly, providing knowledge about the weight that legal decision makers assign to it in forensic settings (Briody, 2003; GoodmanDelahunty & Hewson, 2010;Goodman-Delahunty & Wakabayashi, 2012;Findlay, 2008;Koehler, 2001;Koehler & Macchi, 2004;Kruse, 2012;Lynch, 2013;Smith & Bull, 2012;Smith, et. al., 2011;Wheate, 2006;.…”

Getting scarred and winning lotteries: effects of exemplar cuing and statistical format on imagining low‐probability events

“…In an intriguing article, Koehler and Macchi (2004) speculated that particular statistical formats need not necessarily evoke terrifying or affectively rich imagery to influence probability judgment; it may be sufficient for the statistics to simply evoke thoughts about other examples of the target event. Their 'exemplar cuing (EC) theory' states that, 'the weight decision makers attach to low-probability events is, in part, a function of whether they can easily generate or imagine exemplars for the event' (p. 540).…”

“…Importantly, this mechanism is unaffected by the format of the information, that is by whether incidence rates are provided as percentages (1%) or frequencies (1 out of 100). The reason that format does not affect exemplar generation is that the format does not identify a relevant sample space within which to search for exemplars (Koehler & Macchi, 2004). This sample space is provided by the reference class (e.g.…”