Psychology | Methods
Individual Differences
Quantitative versus Qualitative Differences
Psychological phenomena are typically understood in reference to the mean. We compare means and report effect sizes in terms of standardized mean differences. However, what does the mean actually mean? It is hard to think of an effect which affects every individual in exactly the same way. Typically, people differ. The important question is: Are these differences only quantitative or also qualitative?
Think of an analgesic: If it works better for some people than for others, but it still relieves pain for all, individual differences are only quantitative. In contrast, if some are allergic and their pain actually gets worse after taking the drug, these differences are qualitative. Qualitative differences may imply separate underlying mechanisms. Therefore, it is important to understand the structure of individual differences and distinguish between qualitative and quantitative differences also in the context of psychological phenomena.
In my research, I’m building on previous work by Julia Haaf (Amsterdam) and Jeff Rouder (Irvine). I’m working on applying their approach to specific cognitive phenomena (e.g., the truth effect) and extending it to other common scenarios (e.g., binary data).
