A Plea for Studying Qualitative Individual Differences by Default.

I see great potential in the approach proposed by Rouder and Haaf. First, using an example from unethical decision making, I demonstrate that considering quantitative individual differences alone can make us overlook important psychological phenomena that are only visible at the individual level. Thus, the study of quantitative individual differences should, by default, be complemented by investigation of qualitative individual differences. Second, having powerful tools to study qualitative individual differences in cognition has great potential to advance personality science. Recently, personality psychologists are increasingly working towards obtaining a better understanding of the processes that underlie the expression of personality in behavior. The toolbox provided by Rouder and Haaf may add to this research in meaningful ways.