The effect of latency variables on repeated measures inference applied to the measurement of risk-taking as a function of psychopathy

In numerous psychology studies, subjects are asked to perform some task a number of times, T. The effect of the choice of T on the associated inference, however, is usually not assessed. We investigate the appropriate choice of T empirically by using data collected in a study on the relationship between psychopathy and risk-taking in 90 inner city drug users enrolled in a residential treatment program. We show that, when studying this relationship, the latency variable usually discarded from the analysis behaves exponentially allowing a natural division of the study period 1, . . . , T into two distinct subperiods. These subperiods yield significantly different results—in the early period only (which we call “reactive”), subjects with high psychopathy scores exhibit lower sensitivity to reward and punishment in our risk taking experiment. The later period (which we call “stable”) shows no relationship between sensitivity to reward and punishment and psychopathic tendencies.