Ethan Bolker sends along this news article from the Boston Globe:
If it doesn’t acquit, it must fit
Judges and juries are only human, and as such, their brains tend to see patterns, even if the evidence isn’t all there. In a new study, researchers first presented people with pieces of evidence (a confession, an eyewitness identification, an alibi, a motive) in separate contexts. Then, similar pieces of evidence were presented together in the context of a single criminal case. Although judgments of the probative value of each piece of evidence were uncorrelated when considered separately, their probative value became significantly correlated when considered together. In other words, perceiving one piece of evidence as confirming guilt caused other pieces of evidence to become more confirming of guilt too. For example, among people who ended up reaching a guilty verdict, the same kind of confession was considered more voluntary when considered alongside other evidence than when it had been considered in isolation.
Greenspan, R. & Scurich, The Interdependence of Perceived Confession Voluntariness and Case Evidence, N. Law and Human Behavior (forthcoming).
The tone suggests that this observation—“perceiving one piece of evidence as confirming guilt caused other pieces of evidence to become more confirming of guilt too”—reflects an inability to weigh evidence, but to me it makes Bayesian sense: each piece influences the priors for the others.
I agree. It seems like a judicial example of a familiar tension from statistical analysis: when do we want to simply be summarizing the data at hand, and when do we want to “collapse the wave function,” as it were, and perform inference for underlying parameters.