My understanding is, ideally your clinical trial manages to capture or balance out the different potential factors in genetic variation. An example of this is

My understanding is, ideally your clinical trial manages to capture or balance out the different potential factors in genetic variation. An example of this is when they tested the covid vaccine, they wanted to make sure they had enough participation from African American and other ethnicities since these were usually under represented in clinical trials relative to the population, and there are sometimes subtle variations in the way peoples body respond to drugs depending on their race.