Depends on the goal. If the risk factor is homogenized, then the variable researched can be isolated theoretically. However, this doesn’t allow you to test fo

Depends on the goal. If the risk factor is homogenized, then the variable researched can be isolated theoretically. However, this doesn’t allow you to test for interaction between those variables. In the study for example, they identify an apparent interaction between ethnicity and the chemicals mentioned; we don’t know what the effect size would be (whether additive, multiplicative, or something else entirely). (This is without any domain knowledge of the mechanisms of breast cancer to be fair.)