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Parenthetically Speaking: Colons, Math and the New York Times (repost 2008)

Science, Numbers, Journalism and Critical Thinking

I believe it was on a Merlin Mann podcast, where someone jokingly mentioned the concept of an iColon website which in typical Web 2.0 fashion people could share the images and films of their colonoscopy procedures. This week the New York Times managed to demonstrate where their heads were at regarding simple mathematics and statistics. An article by one of their most popular reporters reviewed a new study that showed that colonoscopies were not all they were cracked up to be as far as picking up colon cancer and in their ability to prevent future cancers from developing from detection and removal of polyps.

The American Cancer Society still strongly recommends the colonoscopy as a useful  screening procedure. and the physicians I know who both perform this procedure and recommend it all strongly feel that it is one procedure that can actually save lives. We will however take a quick and simple look at the use of math and see a lack of simple math skills and the failure of editorial checking at the New York Times.

The NY Times reported on a study that demonstrated that colonoscopy missed virtually all polyps on the right side of the colon. The  article stated that 40% of all cancers and polyps originated on this side. Of those on the left side of the colon up to 30% of those were missed. The article then went on to quote and conclude that rather than preventing up to 90% of colon cancer from devleloping it might only be useful in preventing 60% to 70%. Now, this seems to be a fairly simple math problem. And a quick glance by anyone even one with only minimal math skills just looks and sounds wrong on the surface of it all.

If 40% of the lesions occur on the left side but are undetectable, than you have remaining 60% of the lesions to deal with that you can find. If 1/3 of these ones are not found, by splitting them into 3 equal parts of 20% 20% and 20%, and you remove 1/3 you are then left with 40% of the lesions that you would be able to find.
Hence, it is clear that it is not 60%-70% number of lesions that you’ll expect to find, but a number significantly less than 50% and which clearly looks to be 40%. The physician interviewed in the New York Times encourages people to have the colonoscopy as a screening procedure, but to not necessarily expect to be safe for the next 10 years. It is strongly recommnended that you follow the colon cleaning procedures prescribed prior to undergoing the procedure.

There will be more studies in the future and likely ones that will be quite positive on colonoscopy. Techniques will likely be modified that also result in improved detection of right sided lesions. Until then, we now and always will need clear heads to do the math and keep evidence based medicine, based on evidence and not on an easily obtained quote.

Up soon we may dissect an article published within the last few months that looked at the longevity of runners and non-runners. If you know the study, here’s a hint: check out the disparate population groups studied and see if it looked like a well designed and controlled study.

New Math From the New York Times:

“In the new study, the test missed just about every cancer in the right side of the colon, where cancers are harder to detect but about 40 percent arise. And it also missed roughly a third of cancers in the left side of the colon.

Instead of preventing 90 percent of cancers, as some doctors have told patients, colonoscopies might actually prevent more like 60 percent to 70 percent.”