INVESTIGATED UTILITY THEORY BY HAVING 11 SS BID FOR RISKY OPTIONS. ADDITIVITY ANALYSIS SUPPORTED UTILITY THEORY BUT REJECTED AN ALTERNATIVE ADDITIVE MODEL. THE DATA WERE ACCOUNTED FOR, WITHIN THE LIMITS OF EXPERIMENTAL ERROR, BY A POWER UTILITY FUNCTION WITH DIFFERENT EXPONENTS FOR POSITIVE AND NEGATIVE OUTCOMES. THE UTILITY FUNCTIONS OF MOST SS WERE LINEAR OVER GAINS AND CONCAVE OVER LOSSES. THE SUBJECTIVE PROBABILITY FUNCTIONS OF MOST SS OVERESTIMATED LOW (OBJECTIVE) PROBABILITIES AND UNDERESTIMATED HIGH ONES. THEORETICAL IMPLICATIONS OF THE FINDINGS ARE DISCUSSED. (23 REF.) (PsycINFO Database Record (c) 2006 APA, all rights reserved)