I can see why that is a hard question to answer, considering that bathing is very often a cultural based opinion. Some cultures shun bathing, others really care about hygiene.
I expect you are looking for a medical related advice, as in, what is the recommended amount of showering to ensure safety from catching sicknesses, etc? I'm not sure you will find such an answer other than asking a few doctors yourself on the matter. I personally doubt they have a actual study based answer to give you, this sort of question isn't something many people have probably decided to experiment and find optimum health per shower sort of thing.
I personally think 2-3 times per week is lacking, people very often begin to smell "human" within 2 days I would say. I take 1-3 showers a day minimum, not because of hygiene issues, but I can't stand the idea of going to bed with germs that I picked up all day and smothering my bed with it while I am sleeping with my immune system down, and I need a shower after I wake up to well, wake up. This causes me problems during the wintertime though, I get dry skin as a result of having washed out my natural body oils.
So I'd recommend at least once every day or two days.