An additional complication with evaluating gene-environment interactions in psychology is that often our environmental measures don’t have absolute scales of measurement. For example, what is the “real” metric for measuring a construct like parent-child bonding, or maltreatment, or stress? This becomes critical because fan-shaped interactions are very sensitive to scaling. Often a transformation of the scale scores will make the interaction disappear. What does it mean if the raw variable shows an interaction but the log transformation of the scale scores does not? Is the interaction real? Is one metric for measuring the environment a better reflection of the “real” nature of the environment than another? Many of the environments of interest to psychologists do not have true metrics, such as those that exist for measures such as height, weight, or other physiological variables. This is an issue for the study of gene-environment interaction. It becomes even more problematic when you consider that logistic regression is the method commonly used to test for gene-environment interactions with dichotomous disease status outcomes. Logistic regression involves a logarithmic transformation of the probability of
