Multiplicative treatment effects in randomized pretest-posttest experimental designs

Gender differences in aggression: A multiplicative function of outward anger expression

Individuals with a higher (vs. lower) tendency to outwardly express anger (i.e., greater anger-out) generally exhibit greater aggression; men (vs. women) also tend to be more aggressive. Although the general aggression model posits that multiple person variables trigger aggression, the combined effects of multiple person variables are poorly understood. Thus, the aim of this study was to examine the nature of the relation between gender, anger-out, and reactive aggression. In particular, we were interested in whether the effects of anger-out and gender are additive or multiplicative. Specifically, we tested whether men exhibit higher levels of aggression than women at a consistent ratio across all levels of anger-out (i.e., the multiplicative model) or at a fixed amount depending on the level of anger-out (i.e., the additive interaction model). To this end, undergraduate participants (N = 203) completed a task in which they were falsely instructed that their objective was to respond more quickly than a same-sex opponent. They were told that whoever responded more quickly would administer a white noise burst to the opponent and choose its intensity, which served as our measure of aggression. Compared to an additive interaction model, the multiplicative model exhibited a better fit. Specifically, men displayed proportionately more aggression than women with the same level of anger-out. Research on and treatment for aggression should consider the multiplicative effects of factors related to aggression.