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Keywords: pre mp in psychological experiments than do individualists and competitors. Study 2 replicated these findings, icipate d eco consists of psychology or economics students, we still do not nec-essarily know who they are in terms of relative stable orientations that they bring to the laboratory. For example, is our samples rep-resentative in terms of dispositions such as considerateness, fair-ness, or trust? This is important, because such topics touch upon tic, and competitive orientation) and tendencies to volunteer to participate in psychology experiments. We also examine whether these differences in social value orientation are associated with tendencies to choose psychology or economics as the primary ma-jor for study at the university. Theoretically, the concept of social value orientation extends the ‘‘rational self-interest ” postulate by assuming that individuals systematically differ in their interpersonal preferences, with some seeking to enhance joint outcomes and equality in outcomes (pro-social orientation), and others seeking to enhance their own out-comes in absolute terms (individualistic orientation) o