I did some checks and that appears to be said by Darrell Huff...Are you sure it was Henry G. Felsen?
According to Darrell Huff, it was first said by Henry G. Felson:
As Henry G. Felson, a humorist and no medical authority, pointed out quite a while ago, proper treatment will cure a cold in seven days, but left to itself a cold will hang on for a week.
Huff, Darrell. How to lie with statistics. New York: Norton, 1993.
That answers my question, thanks! In my experience, any citation that does not refer to some printed reference should not be believed—a line saying “as quoted in How to lie with statistics by Darrell Huff” was what I was looking for.
According to Darrell Huff, it was first said by Henry G. Felson:
Huff, Darrell. How to lie with statistics. New York: Norton, 1993.
That answers my question, thanks! In my experience, any citation that does not refer to some printed reference should not be believed—a line saying “as quoted in How to lie with statistics by Darrell Huff” was what I was looking for.