Dealing with unknown dependencies between variables


I have a system where I'm studying 3 different diseases, however they share some pathological similarities. There is no data on them being similar in the properties that I am studying, but of course it cannot be ruled out that the three will share that specific characteristic. So, in this situation should I consider the three diseases to be independent? Or should I assume dependency for the sake of statistical analisys? Is there any rule of thumb in this situation?



Omega Contributor
Yes, it would help if you provided some context of what you are trying to do or control for so we better understand. What are your outcomes and covariates: disease and bioassays/biomarkers?