A study examined the effect of assigned social decision rule (whether a jury is required to give a unanimous or less than unanimous verdict) on the process and product of mock jury deliberations. Subjects, 360 students from an eastern university, were randomly assigned to six-member juries under three decision rule conditions: (1) unanimity, (2) five-sixths majority, and (3) two-thirds majority. After viewing a videotape of a criminal trial, subjects completed a pre-deliberation questionnaire, using the cognitive response method, about the arguments advanced by the prosecution and defense during the trial, and their level of importance to each side. The quantity and quality of arguments recalled were the dependent variables. Subjects then deliberated until the assigned social decision rule was reached. Upon completing deliberation, subjects filled out a post-deliberation questionnaire. The research design employed was a split-plot repeated measures design, with one "between" factor and two "within" factors. Results showed that jurors assigned to unanimous decision conditions recalled significantly more arguments than either majority rule condition, and had significantly higher ratings for the importance of the arguments recalled after deliberation. The findings suggest that unanimous juries are preferable because they recall more ideas to work with in deliberating, and consider the arguments more carefully. Additionally, other members of the jury seem to be persuaded by jurors presenting numerous, compelling, and unique arguments for a particular side. (Six pages of references and eight tables are included.) (JC)