Dateline: June, 2011, Issue 3
The study of jurors' opinion formation and change over the course of trials rarely relies on data from real jurors, and instead most often is based on invesitations of mock jurors or student jurors.
Two studies have explored the verdict preferences of actual jurors who served in many different civil and criminal cases about when they began leaning toward one side or the other, and when they made up their minds about who should prevail.
Hannaford and colleagues (2000) questioned 1,385 jurors from 172 different civil trials, finding that jurors primarily reported beginning to lean toward a side during the three trial segments of plaintiff evidence, defense evidence and jury deliberation, and at similar rates (19-24% for each segment). Jury deliberations were the most significant trial segment in which jurors reported that they made up their minds (46%). Further:
Waters and Hans (2008) questioned 3,497 jurors from 382 different criminal trials, and found a similar pattern: 9% of jurors reported leaning toward one side or another during opening statements, 53% reported forming an opinion during the evidentiary period (particularly during the prosecution's case), and 20% said they only began leaning toward one side once they deliberated with other jurors. Interestingly, when a majority of jurors voted to acquit the defendant, only 15% of jurors reported they were undecided at the time of deliberations, while more jurors (21%-24%) on juries with a majority to convict or that hung on a charge said they waited until final deliberations to lean toward one side in the case. Most jurors (62%) reported changing their mind at least once during the trial, with 18% changing their mind during the prosecution's case, and 25% during deliberations. A jury's first vote strongly resembled a jury's final vote: almost 90% of the time when a substantial majority (at least 8 of 12, for example) favored either conviction or acquittal on the first vote, the jury ultimately reached that decision on the final vote. Juries with first ballot votes that were closely split (6-6, or 5-7, for example) overwhelmingly shifted to either an acquittal or conviction by the final vote in deliberations (80%), and were also more likely to hang on at least one charge.
In sum, relatively few jurors begin leaning toward one side or the other during opening statements, many jurors begin leaning toward one side or the other during the presentation of evidence, over half of all jurors report making up their minds prior to deliberations, and a jury's first ballot is often highly indicative of the final verdicts.
Source Hannaford, P.L., Hans, V.P., Mott, N.L., & Munsterman, G.T. (2000). The timing of opinion formation by jurors in civil cases: An empirical examination. Tennessee Law Review, 67, pp. 627-652.
Source Waters, N.L. & Hans, V.P. (2008). A jury of one: Opinion formation, conformity, and dissent on juries. Cornell Legal Studies Research Paper 08-030.