THE WILLIAMS-JOHNSON-APODACA-COLGROVE SEQUENCE OF SUPREME COURT OPINIONS PERMITTING THE REDUCTION OF JURY SIZE TO SIX IN FEDERAL CIVIL TRIALS AND STATE CRIMINAL TRIALS AND ALLOWING MAJORITY VERDICTS IN STATE CRIMINAL TRIALS HAS BEEN UNCRITICAL AND INCOMPETENT IN TREATING EMPIRICAL EVIDENCE AND UNFAITHFUL TO COMMON LAW IN REDUCING THE PROTECTIVE FUNCTION OF TRIAL BY JURY. THE BEST EVIDENCE ON JURY DECISIONMAKING SHOWS THAT THE PURPOSE AND FUNCTIONING OF THE JURY IN A CRIMINAL TRIAL IS SERIOUSLY IMPAIRED TO A CONSTITUTIONAL DEGREE BY A SIZE REDUCTION TO SIX. THIS IMPAIRMENT AFFECTS GROUP DELIBERATION; THE ACCURACY, CONSISTENCY, AND RELIABILITY OF DELIBERATION RESULTS; SUPPORT FOR THE MINORITY JUROR; THE QUALITY OF COMMUNITY PARTICIPATION AND REPRESENTATIVENESS; AND THE SUBSTANTIAL EFFECTS OF SMALL PERCENTAGE DIFFERENCES IN THE OUTCOMES OF DELIBERATIONS BETWEEN THE 12- AND 6-PERSON JURIES. THE HIDDEN REASONS FOR THE COURT'S DECISIONS CONCERNING JURY SIZE MAY LIE IN THE DESIRES TO LIMIT JURY COSTS, DECREASE COURT DELAY TIME, INCREASE JUDICIAL POWER, AND INCREASE THE NUMBER OF CRIMINAL CONVICTIONS. SUCH REASONS DO NOT QUALIFY AS A RATIONALE FOR REDUCING THE EFFECTIVENESS OF THE DECISIONMAKING POWER OF CITIZENS IN THE JUDICIAL PROCESS. FOOTNOTES ARE PROVIDED. (RCB)