THE OFFENSE SERIOUSNESS SCALING SYSTEM IN QUESTION ASSUMES THAT A SERIOUSNESS RATING FOR A MULTIPLE OFFENSE (E.G., TWO PURSE-SNATCHINGS) CAN BE ACCURATELY OBTAINED BY COMBINING THE RATINGS FOR EACH ELEMENT (EACH PURSE-SNATCHING) OF THE OFFENSE. TO TEST THIS ASSUMPTION IT IS NECESSARY TO KNOW WHETHER PEOPLE VIEW A MULTIPLE OFFENSE AS LESS SERIOUS THAN, EQUALLY SERIOUS AS, OR MORE SERIOUS THAN A SINGLE, IT IS NECESSARY TO KNOW EXACTLY HOW MUCH MORE SERIOUS. FOUR HYPOTHETICAL CASES, EACH DESCRIBING A SINGLE AND A DOUBLE OFFENSE (E.G., ONE OFFENDER SNATCHES A PURSE CONTAINING $2.00, WHILE A SECOND OFFENDER SNATCHES TWO HANDBAGS EACH CONTAINING $2.00), WERE PRESENTED TO 111 ENGLISH COLLEGE STUDENTS, WHO WERE ASKED TO JUDGE THE RELATIVE SERIOUSNESS OF THE OFFENSES. (OTHER HYPOTHETICAL CASES INVOLVED STABBINGS, RAPES, AND ARMED ROBBERIES.) IN ONLY 18 PERCENT OF THE JUDGMENTS WAS THE DOUBLE OFFENSE REGARDED AS EXACTLY TWICE AS SERIOUS AS THE SINGLE OFFENSE. FOR MOST RATERS (75.2 PERCENT), THE FACT THAT TWO OFFENSES WERE COMMITTED TOGETHER REDUCED THE JUDGED SERIOUSNESS OF EACH OFFENSE INDIVIDUALLY. IN 65.3 PERCENT OF THE JUDGMENTS, COMBINED OFFENSES WERE REGARDED AS EQUALLY SERIOUS AS SINGLE OFFENSES. THE FINDINGS SUGGEST THAT THE ADDITIVITY ASSUMPTION IS INCORRECT. TABULAR DATA AND A LIST OF REFERENCES ARE INCLUDED. (LKM)