Variations on the "but we don't know which half" line

I first heard it attributed to a University of Chicago President addressing an incoming Freshman class: "Half of everything we teach you is wrong... unfortunately, we don't know which half." But it appears to have an even longer history in advertising.

EDUCATION

Donald McCoy DVM: When I attended Veterinary School in 1970, we were told that half of what we learned might not be true, but we just didnšt know which half.
Richard Ruhling, MD: One of my professors, John Peterson, MD, was taught at Harvard that half of medical education was not true, the only problem was, they didn.t know which half
John L. Meade, MD, FACEP: When I started medical school, a professor told us that half of what we would be taught in the next 4 years was wrong; unfortunately, we didn't know which half was wrong just yet.
(???:) My wife is a practicing doctor. And in general we have high respect for the medical field. However, as she was going through her medical training at one of the top medical schools in the USA, she was told that half of what she would be taught over the next 4 years would later be found to be inaccurate, they just didn.t know which half.

ADVERTISING

Rance Crain: I always thought it was only the advertising industry that believed half of what it spent, or knew, or did was wasted -- they just didn't know which half. Then I read a New York Times Magazine article about medical progress, or lack thereof. The doctor who wrote it said that at her "white-coat ceremony," welcoming her class to med school, the dean proclaimed half of what the school teaches is wrong -- only they don't know which half.
Robert Loch: Lord Lever once said (although often attributed to Henry Ford) that he knew that only half his advertising worked, but the trouble was that he didn.t know which half.
"John Wanamaker once said he knew half of his advertising was wasted, he just didn't know which half," Cynthia Ponce, EVP, ABC Television Network Sales
Peter Bowditch: I expect many to be quoting the Lever brother who said that half his advertising was wasted but he didn't know which half.
Walt Patrick: It's like Kornbluth's Law. He observed 1) that he knew that half the money he spent on advertising was wasted and 2) that he didn't know which half it was.
link The statement attributed to the legendary carmaker Henry Ford comes to mind. He claimed that half of his advertising budget was wasted - but he didn't know which half!
Clive Thompson: John Wanamaker, a department-store magnate in the late 19th century, famously quipped that half the money he spent on advertising was wasted, but that he didn't know which half.
link As Henry Ford once said, he knew half of every dollar he spent on advertising was wasted. He just didn't know which half.
Clive Webster: Lord Leverhulme once said he knew half of his advertising was wasted, but didn't know which half.
Andrea Popp: In one of the marketing textbooks from my college days, I remember an interesting story about department store tycoon J.C. Penney. He once stated he was aware of the fact that only fifty percent of his advertising was working. When an associate asked him why he continued to do all of his advertising efforts when he knew only half of it was working, he replied that he didn.t know which half of his advertising wasn.t working!
Art Menius: In the 1880s, Philadelphia department store giant John Wanamaker said that he knew half his ad budget was wasted, but he didn.t know which half.