Tue, Jan-06-09, 10:35
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Experimenter
Posts: 25,863
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Plan: DDF
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BF:
Progress: 72%
Location: San Diego, CA
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Observational Studies
Dr. Eades posting on the uselessness of epidemiological studies.
http://www.proteinpower.com/drmike/...onal-studies-2/
Snippet
Quote:
If you want to bear with me, I’ll show you a bizarre observational study that was actually performed that demonstrates everything you need to know about observational studies.
The study was published in 2003 in the prestigious American Journal of Epidemiology. The title of the study is Shaving, Coronary Heart Disease, and Stroke. (Click here for free full text) This study purports to show that the frequency of shaving correlates with risk for developing heart disease, with those men shaving less having a greater risk.
Here’s the finding that initiated this study.
A case-control study comparing the frequency of shaving in 21 men under 43 years of age who had suffered a myocardial infarction and 21 controls found that nine of the cases but none of the controls shaved only every 2 or 3 days.
Someone noticed that about half of the men in a small group of subjects who had a heart attack shaved once every two or three days. Another group of men of similar age who hadn’t had a heart attack were designated as controls. Upon questioning it was discovered that all of the men in the control group shaved every day. Thus the first hypothesis was born: Infrequent shaving correlates with heart attack.
The researchers had access to a large population of subjects from another ongoing study called the Caerphilly Study. Researchers recruited 2,513 men aged 45-59 from this study and gave them comprehensive medical workups including extensive laboratory testing.
Men were asked about their frequency of shaving by a medical interviewer during phase I. Responses were classified into categories ranging from twice daily to once daily, every other day, or less frequently. The 34 men with beards were not classified. These categories were dichotomized into once or twice per day and less frequently.
The men in the study were followed for the next 20 years with follow-up exams periodically to monitor for history of chest pain, heart attack and/or stroke.
Of the 521 men who shaved less frequently than daily, 45.1 percent died during the follow-up period, as compared with 31.3 percent of men who shaved at least daily.
When the data were further refined it was determined that
The age-adjusted hazard ratios demonstrate increased risks of all-cause, cardiovascular disease, and non-cardiovascular-disease mortality and all stroke events among men who shaved less frequently.
So there you have it. Proof that shaving daily prevents heart disease. Or is it?
The researchers doing this study aren’t so stupid that they really think that the act of shaving itself has anything to do with a man’s risk for developing heart disease. In fact, they went to great lengths to show that shaving was merely a marker for other things going on that may well have something to do with risk for developing heart disease or increased all-cause mortality.
The one fifth (n = 521, 21.4%) of men who shaved less frequently than daily were shorter, were less likely to be married, had a lower frequency of orgasm, and were more likely to smoke, to have angina, and to work in manual occupations than other men.
And these are just the differences the researchers found. Had they looked harder, I’m sure they would have found more, just like I did when I played my ‘think of everything that can be thought about’ game with myself as a kid.
But if these researchers had really believed that the data showed that the lack of frequent shaving itself may have been the driving force behind the development of heart disease, they may have designed a randomized clinical trial to show causality. They could have recruited men without heart disease, randomized them into two groups, instructed the men in one group to shave daily and the men in the other to shave every third day. Then after 20 years the researchers could tell whether or not shaving protects against heart disease.
But the idea that shaving itself has anything to do with heart disease is so ludicrous that no one would ever do such a study. We can all see that. It’s a ridiculous idea. It should be obvious that the shaving or lack thereof has nothing to do with heart disease or early death; the lack of shaving is merely a marker for all the other conditions that are risk factors for heart disease, i.e., small stature, unmarried, smoking, lower socioeconomic class, etc. It’s all so easy to see.
But let’s just suppose that we take this same study and substitute the term ‘elevated cholesterol’ for ‘infrequent shaving.’ Now what do we see? Let’s change one of the quotes from above to reflect this change. What then?
Of the 521 men who had elevated cholesterol, 45.1 percent died during the follow-up period, as compared with 31.3 percent of men who had low or normal cholesterol.
We nod our heads sagely. Suddenly we have a study that seems to make sense. But - and this is important - it doesn’t make any more sense than the shaving study. Both are observational studies. We are programmed to think cholesterol is bad and causes heart disease, so this second study appears reasonable to us. It triggers our confirmation bias. We don’t believe for a second that shaving has anything to do with heart disease, so we can easily dismiss those findings. But we are more than ready to believe that the elevated cholesterol caused those men who had to have heart attacks. But the reality is that both studies are exactly the same - and neither proves anything.
If you’re interested in a longer, more in-depth article on observational studies, take a look at Gary Taubes long piece in the New York Times a few years ago. I’ve tried to take a little different slant than he did so that my post and his article would cover all the bases.
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Last edited by Nancy LC : Tue, Jan-06-09 at 10:49.
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