craftyguy truncated the comment. "...common in the population between..." those who do and those who do not. I was talking about the water and breathing comment

craftyguy truncated the comment. "...common in the population between..." those who do and those who do not. I was talking about the water and breathing comment, clearly meaning that both the diseased and the unaffected have the behaviors of drinking water and breathing air in common. It's not absolute frequency that matters, but a difference in frequency between the diseased and the disease-free that is potentially explanatory.