A Comparison of Three Types of Insanity Defenses on Juror Decision-Making

This study compared mock jurors' verdict decisions regarding three different insanity defenses that are used across jurisdictions in the United States' Criminal Justice System. Not Guilty By Reason of Insanity (NGRI), Guilty Except Insane (GEI) and Guilty But Mentally Ill (GBMI) all have different effects on the defendant and on the system, but little is known about how jurors' will use these different verdicts. This study used a vignette and online survey delivered through MTurk to see which of the three verdicts, if rendered, would be more preferable by the mock jurors. It was predicted that GEI (a "compromise" verdict with elements from both NGRI and GBMI) would be more favorable than NGRI (the most lenient) but less favorable that GBMI (the strictest). However, the findings indicated that lay people cannot tell the difference between the three insanity verdicts: an equal proportion of mock jurors in each condition chose the relevant insanity verdict. Limitations, implications, and future directions are discussed.