• 14 September 2009

Taking a Stand on Taking the Stand: The Effect of a Prior Criminal Record on the Decision to Testify and on Trial Outcomes

Theodore Eisenberg & Valerie P. Hans

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The evidentiary treatment of a defendant’s prior criminal record is a critically important issue for the criminal justice system and for the day-to-day conduct of criminal cases.  Every year, prosecutors and police are undoubtedly influenced by the existence of prior records in charging and arrest decisions.  At trial, judges exercise substantial discretion in considering the admissibility of defendants’ prior records in thousands of criminal cases.  Fact-finders want to hear defendants provide their own accounts of involvement or lack of involvement in the crime.  Defendants must consider their prior criminal records when they make the key decision of whether to testify because their criminal convictions may be used to impeach their credibility if they take the stand.

All United States jurisdictions allow the use of some criminal convictions to impeach the credibility of a witness.1 Indeed, the impeachment of witnesses with their prior records was permitted at common law as early as the seventeenth century.  Before then, defendants who were convicted felons were prohibited from taking the stand because their testimony was seen as having no credibility.  The existence of felony (and some other) convictions led to the inference that the witness was highly likely to lie under oath.  Over time, jurisdictions eventually eased the prohibition to permit defendants with records to testify, yet simultaneously allow the impeachment of defendants with their prior convictions.

The evidentiary topic of when to permit the fact-finder to learn of a prior criminal record is important because a prior record is thought understandably to promote convictions.  Evidentiary rules try to balance a defendant’s interest in testifying and the prejudicial effect of impeaching the defendant’s testimony using prior convictions.  For example, Federal Rule of Evidence 609(a)(1) allows impeachment by prior convictions “if the court determines that the probative value of admitting this evidence outweighs its prejudicial effect to the accused . . . .”  The judges’ balancing of evidence’s probative value versus possible prejudice should consider the best possible information about the impact of criminal records.  More importantly, a prior criminal record’s obvious prejudicial effect may contribute to the increasingly visible problem of erroneous convictions.

Previous research conducted largely with mock juries suggests several theoretical avenues by which a defendant’s criminal record might bias the fact-finder’s decision to convict or acquit.  It might function as the legal rules governing its use suggest it usually should, by affecting the credibility of the defendant as a witness in the proceedings.  Second, a decision maker might use a defendant’s criminal record to categorize the defendant as a bad person, a person of poor character, creating a negative halo effect.  Third, the weight and significance of the evidence may change; evidence that seems inconclusive against a defendant with no record of wrongdoing may appear to be more damning when jurors learn of the defendant’s criminal past.  Finally, the threshold for conviction, or the subjective burden of proof, may differ for defendants with and without criminal records.  Jurors may be willing to convict on less evidence when the defendant has a criminal past.

Limited empirical analysis exists of the defendant’s decision to testify or of the effect of a prior criminal record on trial outcomes in real jury trials.  Our study uses a unique data set gathered by the National Center for State Courts (NCSC) under a grant from the National Institute of Justice (NIJ) to explore when criminal defendants testify and the effect of that testimony on jury verdicts.2 The data set includes extensive case information and questionnaire responses from trial judges and jurors in 382 felony jury trials in four U.S. jurisdictions.  This data set is especially useful for our purposes because it includes verdict information as well as information about the defendant’s criminal record and whether he or she took the stand.  In addition, both judges and jurors in the felony trials provided their perceptions of the defendant and their estimates of the strength of the evidence in the case.


Our analyses confirm that defendants with and without criminal records testify at different rates; furthermore, the likelihood of learning about a defendant’s criminal record is strongly linked to whether the defendant takes the stand.  In the felony jury trials in the NCSC data set, 60% of defendants without criminal records testified compared to 45% 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.  Statistically significant associations exist (1) between the presence of a criminal record and the decision to testify at trial, and (2) between the defendant testifying at trial and the jury learning about the defendant’s prior record.

We also find that the fact-finder’s knowledge of a defendant’s criminal record is linked to conviction rates in weak (but not strong) cases.  Regression analyses that controlled for a variety of relevant factors show that in cases with strong evidence against defendants, learning of criminal records is not associated with conviction rates.  Instead, juries appear to rely on criminal records to convict when other evidence in the case normally would not support conviction.  In weak cases, those with evidence less than or equal to 3.5 on a rating scale in which 1 represents very weak and 7 represents very strong evidence, the dominant tendency is not to convict.  But, in the strongest of weak cases, the existence of a prior criminal record can prompt a jury to convict.  The prior record effectively leverages the existing evidence over the threshold needed to support conviction.  The effect in otherwise weak cases is substantial and can increase the probability of conviction to over 50% when the probability of conviction in similar cases without criminal records is less than 20%.

As for whether a prior record changes the weight or meaning of evidence, we hypothesized based on mock jury research that knowledge of criminal history could directly affect the jurors’ perceptions of evidentiary strength.  Yet its impact might be difficult to detect because, if it operates as hypothesized, it would already be part of jurors’ perceptions of the strength of the case.  With that as a cautionary comment, the relation between evidentiary strength and knowledge of a criminal record seems more consistent with the threshold theory.  Cases in which jurors learned of criminal records tend to have slightly lower perceived evidentiary strength than cases in which jurors lacked knowledge of criminal records.  Perhaps prosecutors viewed existence of prior convictions as warranting prosecution of otherwise weaker cases.

In addition to the lower conviction threshold, we also find some evidence of a negative halo effect.  Jurors rated their sympathy for the defendant on a seven-point scale.  In a regression model of the degree of sympathy as a function of knowledge of a criminal record, there was a statistically significant negative association between sympathy and record.  But adding the degree of sympathy as an explanatory variable for verdicts in close cases does not yield a statistically significant coefficient for jurors’ perceptions of defendant sympathy.  Jurors may feel more negatively about defendants with criminal records, but that reduced sympathy does not help explain the conviction pattern in close cases.

With respect to the effect of prior record on credibility, we do not find evidence that criminal records affect defendant credibility.  Jurors were asked to rate the believability of the defendant’s evidence on a seven-point scale.  In cases in which defendants testified, criminal record was not significantly associated with the degree of believability.  This non-effect may of course be attributable to defendants being selective about cases in which they testified.  In cases in which testifying would be most damaging to credibility, defendants may simply decline to testify.  However, it is worth noting the convergence of this finding with experimental research.  In mock-jury experiments, researchers have not typically found strong links between the presence of a criminal record and changes in the defendant’s credibility.


Let us consider the results in light of theoretical reasons suggesting why a prior record is important.  Subject to the limitations of a non-experimental design, our findings most directly support the explanation that the conviction threshold appears to differ for defendants with and without criminal records.  The regression models suggest that jurors appear willing to convict on weaker evidence when the defendant has a criminal past.  A prior record plays little role in cases with strong evidence.  Nor does prior criminal record often play an outcome determinative role in cases with extremely weak evidence.  But for cases with evidentiary strength close to, but below, the threshold, a prior criminal record can lead to conviction.  One could view the prior record as “making up” for evidentiary deficiencies.  Or, one might view the prior record as evidence tending to suggest guilt.  Under either view, the prior record makes a difference.  The fact that the record effect occurs primarily in cases where the evidence is not overwhelming converges with the classic finding in judge-jury disagreement studies that extralegal factors operate to cause disagreement primarily in close as opposed to clear cases.

The absence of an association between criminal record and credibility is deeply troubling given the theory underlying allowing impeachment based on a defendant’s criminal record.  In most instances, the justification for allowing the use of prior criminal record is to facilitate assessing the defendant’s credibility.  If, as our results and experimental results suggest, prior record affects case outcomes, but not credibility, the historical justification for allowing use of criminal records is unfounded.


Experimental and real-world data, as confirmed by this study, uniformly indicate that knowledge of a defendant’s prior record promotes conviction in close cases, those where one should be most concerned about erroneous conviction.  The criminal record effect could be even stronger than we have found in these analyses; the experimental work suggests that having a record for a similar offense creates the most bias, and we only had information about the presence of a defendant’s criminal record, not its type.  Together, our results and experimental results indicate that the historical basis for allowing prior record evidence—to challenge the defendant’s credibility—has little empirical support.

The enhanced conviction probability that prior record evidence supplies in close cases may well contribute to erroneous convictions.  As of this writing, over 300 post-conviction exonerations have been documented.3 A recent analysis of DNA exonerations suggests that many erroneously convicted defendants refrain from testifying because they fear the negative consequences of having their criminal records made known to the jury; at the same time, juries who learn of the criminal records of innocent defendants who do testify are likely biased by the record information.4 This suggests the value of exploring the development of legal rules that encourage defendants, even those with criminal records, to testify.  While eliminating all testimony about prior criminal records is unrealistic, prosecutors making charging decisions and judges considering the prejudicial effect of prior records should take into account the dramatic effect that knowledge of a criminal record appears to have in close cases.  Similarly, criminal defense attorneys should think long and hard about having clients testify in what they believe juries might regard as close cases.dingbat



Copyright © 2009 Cornell Law Review.

Theodore Eisenberg is Henry Allen Mark Professor of Law at Cornell University Law School.

Valerie P. Hans is Professor of Law at Cornell University Law School.

This Legal Workshop Editorial is based on the following full-length Article:   Theodore Eisenberg & Valerie P. Hans, Taking a Stand on Taking the Stand: The Effect of a Prior Criminal Record on the Decision to Testify and on Trial Outcomes, 94 CORNELL L. REV. ___ (2009).

The full Article provides documentation and details of the statistical analyses.

  1. GEORGE FISHER, EVIDENCE 265-95 (2d ed. 2008) (discussing impeachment with criminal record).
  2. PAULA L. HANNAFORD-AGOR, VALERIE P. HANS, NICOLE L. MOTT & G. THOMAS MUNSTERMAN, ARE HUNG JURIES A PROBLEM? 29-40 (National Center for State Courts Sept. 30, 2002) (describing the collection and analysis of the data set used in the present study).
  3. Samuel R. Gross & Barbara O’Brien, Frequency and Predictors of False Conviction: Why We Know So Little, and New Data on Capital Cases, 5 J. EMPIRICAL LEGAL STUD. 927, 956 (2008) (describing the frequency and apparent causes of erroneous convictions).
  4. John H. Blume, The Dilemma of the Criminal Defendant with a Prior Record—Lessons from the Wrongfully Convicted, 5 J. EMPIRICAL LEGAL STUD. 477, 486, 490-91 (2008) (finding that 91% of factually innocent defendants with prior records declined to testify, and that counsel in these cases reported that the primary reason was to avoid jury bias stemming from the prior record).

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