This Article uses unique data from over 300 criminal trials in four large counties to study the relations between the existence of a prior criminal record and defendants testifying at trial, between defendants testifying at trial and juries’ learning about criminal records, and between juries’ learning about criminal records and their decisions to convict or acquit. Sixty percent of defendants without criminal records testified, compared to fortyfive percent with criminal records. For testifying defendants with criminal records, juries learned of those records in about half the cases. Juries rarely learned about criminal records unless defendants testified. After controlling for evidentiary strength and other factors, statistically significant associations exist (1) between the existence of a criminal record and the decision to testify at trial, (2) between the defendant’s testifying at trial and the jury’s learning about the defendant’s prior record, and (3), in cases with weak evidence, between the jury’s learning of a criminal record and conviction. For cases with strong evidence against defendants, learning of criminal records is not strongly associated with conviction rates. Juries appear to rely on criminal records to convict when other evidence in the case normally would not support conviction. Use of prior-record evidence may therefore lead to erroneous convictions. We also find little evidence that prior-record information influences credibility. This casts doubt on the historical justification for prior-record evidence: its presumed effect on defendant-as-witness credibility. Prosecutors and judges should consider the increased likelihood of erroneous conviction based on the use of prior convictions in decisions to prosecute and in evidentiary rulings.
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