I did some checks and that appears to be said by Darrell Huff. Links below:
http://www-stat.wharton.upenn.edu/~steele/HoldingPen/Huff/Huff.htm
http://motd.ambians.com/quotes.php/name/linux_medicing/toc_id/1-1-20/s/47
Are you sure it was Henry G. Felsen?
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.
Here's the new thread for posting quotes, with the usual rules: