A meta-analytic review of the weapon focus effect

This meta-analytic review examined 19 tests of the weapon focus effect—the hypothesis that the presence of a weapon during commission of a crime will negatively affect an eyewitness's ability to later identify the perpetrator. A significant overall difference between weapon-present and weaponabsent conditions was demonstrated, with weapon presence leading to reduced identification accuracy. Overall, the size of the effect was small (.13) for the dependent measure of lineup identification and moderate (.55) for feature accuracy. Discussion focuses on those factors that appear to mediate and facilitate the weapon focus effect. This research was supported by a grant from the Bush Foundation through Augsburg College.     

The Impact on Juror Verdicts of Judicial Instruction to Disregard Inadmissible Evidence: A Meta-Analysis

The effect on juror verdicts of judicial instructions to disregard inadmissible evidence was evaluated using meta-analysis. One hundred seventy-five hypothesis tests from 48 studies with a combined 8,474 participants were examined. Results revealed that inadmissible evidence (IE) has a reliable effect on verdicts consistent with the content of the IE. Judicial instruction to ignore the inadmissible evidence does not effectively eliminate IE impact. However, if judges provide a rationale for a ruling of inadmissibility, juror compliance may be increased. Contested evidence ruled admissible accentuates that information, resulting in a significant impact on verdicts. Suggestions for how the courts may mitigate the impact of inadmissible evidence more effectively are discussed.