THE DATA FOR THE DECISIONMAKING MODEL WERE TAKEN FROM AN EXPERIMENT INVOLVING 128 SUBJECTS FROM AN INTRODUCTORY PSYCHOLOGY COURSE, WHO WERE UNAWARE OF THE PURPOSE OF THE STUDY. SUBJECTS WERE ASSIGNED TO EITHER A THREE-PERSON OR SIX-PERSON JURY, BUT OWING TO THE LATE ARRIVAL OF SOME SUBJECTS, FOUR GROUPS OF FIVE-PERSON JURIES WERE ALSO CONSTRUCTED. ALL JURIES READ AND DISCUSSED, IN TURN, FOUR CIVIL CASES THAT HAD BEEN COUNTERBALANCED FOR ORDER OF PRESENTATION. EACH OF THE CASES INVOLVED A DISPUTE BETWEEN AN INDIVIDUAL AND AN ORGANIZATION OR INSTITUTION. THE SUBJECTS WERE INSTRUCTED TO DECIDE FOR OR AGAINST THE PLAINTIFF IN EACH OF THE FOUR CASES IN FOUR SEPARATE CONTEXTS DEFINED FOR THE SUBJECTS. USING A SCALE, THEY WERE TO RATE THEIR CONFIDENCE IN THEIR DECISION, IN THREE OF THOSE CONTEXTS. THE DECISIONMAKING MODEL DERIVED FROM THE DATA IS ONE IN WHICH: (1) THE APPARENT WEIGHT OF EVIDENCE TO A JUROR DECIDING ON A CASE VARIES RANDOMLY OVER THE POPULATION OF POTENTIAL JURORS; (2) JURORS DECIDE FOR (AGAINST) THE PLAINTIFF OR DEFENDANT IF APPARENT WEIGHT OF EVIDENCE IS LESS (GREATER) THAN A DECISION CRITERION (BEYOND A REASONABLE DOUBT, ETC.), WHICH VARIES LITTLE OVER THE POPULATION, BUT MAY VARY OVER CASES, INSTRUCTIONS TO JURORS, ETC.; AND (3) DECISION CONFIDENCE INCREASES AS ABSOLUTE DIFFERENCE BETWEEN APPARENT WEIGHT OF EVIDENCE AND DECISION CRITERION INCREASES, WITH THIS INCREASE TAKEN AS LINEAR FOR MOST OF THE PRESENTATION. IT IS ASSUMED THAT THE DISTRIBUTION OF APPARENT WEIGHT OF EVIDENCE IS BASED ON THE EXPONENTIAL DISTRIBUTION, AND ESTIMATES OF MEAN APPARENT EVIDENCE WEIGHT AND DECISION CRITERIA ARE OBTAINED FROM THE FOUR CIVIL CASES OF THE EXPERIMENT AND TWO ADDITIONAL CRIMINAL CASES. THE EFFECTS OF JURY DELIBERATION, JURY SIZE, THE DEFINITION OF 'REASONABLE DOUBT,' THE INTRODUCTION AS EVIDENCE OF A PREVIOUS RECORD OF CONVICTION, AND INSTRUCTIONS TO DISREGARD SUCH EVIDENCE ARE DESCRIBED IN TERMS OF THE PARAMETER ESTIMATES. FINALLY, THE THEORETICAL RELATIONSHIP BETWEEN DECISION FREQUENCY AND CONFIDENCE IS DISCUSSED, AND A MEASURE IS GIVEN OF THE DIFFERENCE BETWEEN THE SUBPOPULATIONS OF JURORS VOTING 'FOR' AND 'AGAINST.' IT IS SHOWN THAT THIS DIFFERENCE MEASURE EQUALS THE AREA UNDER A CONFIDENCE-RATING OPERATING CHARACTERISTIC CURVE. CASES ARE DETAILED IN AN APPENDIX. (AUTHOR ABSTRACT MODIFIED--RCB)