In psychology, there is no such thing as a perfect experiment. Often, it is clear from the get-go that there are certain problems (“confounds”) you will not be able to eliminate, no matter how sophisticated your design might be. The remedy is simple and straightforward: measure what you can measure and try to statistically control for these variables. From some enthusiastic applications, I find that the number of covariates appears to be proportional to the degree you want to show off to other researchers how deeply you care about your data. As a psychologist, I can say that we love and embrace covariates (and subtle, yet significant interaction terms, but this practice had some bad press lately). The belief in the statistical procedure of control via covariates thus seems to be deeply rooted in practice, a bit of everyday numerical magic. Continue reading “Covariate magic part 1: That has been accounted for by the covariate!”
It’s about magic, or something very close to magic: statistical control. Neurocopiae talks covariates.