THE EFFECTS OF ASSIGNED DECISION RULES OF THE CURRENT AND PROPOSED GRAND JURY SYSTEMS, ALONG WITH RESPECTIVE ALLOWABLE SIZE RANGES, ARE ANALYZED AS PRESENTED IN TWO BILLS INTRODUCED IN THE 95TH CONGRESS (S 1449 AND HR 94). SOCIAL-DECISION-SCHEME MATRIXES FOR THE MAXIMUM AND MINIMUM GRAND JURY SIZES UNDER THE CURRENT SYSTEM AND UNDER THE SYSTEM PROPOSED IN HR 94 SHOW THAT BY FIXING THE CRITICAL NUMBER FOR INDICTMENT AND ALLOWING SIZE TO VARY, A DIFFERENT SOCIAL DECISION SCHEME RESULTS AT EACH SIZE CHANGE IN THE GRAND JURY. THUS, A SET OF JURORS NEAR THE MAXIMUM OF 23 UNDER THE CURRENT SYSTEM IS MORE LIKELY TO YIELD AN INDICTMENT THAN A SMALLER JURY NEAR THE MINIMUM OF 16 MEMBERS. UNDER THE PROPOSED REFORM, A CONSIDERABLE SIZE EFFECT OVER THE RANGE OF GRAND JURY SIZES IS ALSO EXHIBITED, BUT A SMALLER GRAND JURY IS MORE LIKELY THAN A LARGER ONE TO INDICT WHEN THE PROBABILITY OF INDICTMENT IS SMALL. THE SMALL JURY IS LESS LIKELY TO INDICT WHEN THE PROBABILITY OF INDICTMENT IS LARGE (DUE TO THE FIXING OF THE PROPOSED DECISION RULE AT TWO-THIRDS OF THOSE PRESENT WHO ARE VOTING). A MATRIX CONSTRUCTED TO DETERMINE THE EFFECT OF A TWO-THIRDS RULE ON THE CURRENT GRAND JURY SYSTEM PRODUCED AN EVEN LOWER PROBABILITY OF INDICTMENT THAN THE PROPOSED TWO-THIRDS DECISION RULE OVER MOST OF THE RANGE OF INDIVIDUAL PREFERENCE. CONCLUDING REMARKS ON THE USE OF EMPIRICAL DATA FROM RESEARCH IN IMPLEMENTING SOCIAL REFORMS IDENTIFY TWO CONTINUING DIFFICULTIES: (1) RESEARCHERS CANNOT GENERATE AN EMPIRICAL STUDY FOR EVERY LEGAL QUESTION THAT MIGHT ARISE DUE TO CHANGES IN SOCIAL BEHAVIOR; AND (2) EVALUATION OF INSTITUTIONAL OR PROGRAM CHANGES PRIOR TO IMPLEMENTATION IS FACED WITH MAKING DECISIONS BEFORE THE CHANGES THAT WILL SUPPLY THE NECESSARY EVALUATIVE DATA HAVE OCCURRED. REFERENCES ARE PROVIDED. (DEG)