Please assume that I have two metric independent variables (e.g., two blood parameters), and a dependent variable (e.g., a disease). On the DV, 0 represents the absence from the disease, 1 represents a weak occurrence ... 10 (max.) represents a very strong occurrence (please ignore the usefulness of such an assessment). The supposed problem comes in because in my sample (N = 80), only 25% score > 0 on the DV (that is, 20 participants).
Anyway, I regressed (OLS and Tobit) the DV on IV1, IV2, and the interaction of IV1 and IV2. The interaction turns out to be significant, no main effects occured. Because of the low baseline (25% > 0 on the DV), is this procedure considered problematically? Is my baseline too low? Are there not enough participants having the disease?
Let us assume, ideally, that all of the 20 participants score between 8-10 (DV) and all 20 have a special pattern of the IVs, e.g., low IV1 and low IV2, so this group, simplified, is compared to # low IV1 and high IV2; # low IV1 and low IV2; # high IV1 and high IV2. So from my understanding, a group of 20 is compared against, ideally, 3 groups of 20 participants, which is quite common in medical research. So do you think there are problems? And any literature suggestions that I am “allowed” (or not allowed) to analyze the data the way I do?
Well, because I'm not an expert I hope that you can turn on the lights for me … Thanks!