[postfuturist]

This sort of 'science writing' is infuriating:

"Specifically, he found that men who reported more than 23 hours a week of sedentary activity had a 64 percent greater risk of dying from heart disease than those who reported less than 11 hours a week of sedentary activity. And many of these men routinely exercised."

Well, is he controlling for those who exercise or not? If not, then what is the point?

[niels_olson]

As a physician, I find NPR is generally good at addressing issues at a level the average person can understand. No one is claiming the NPR article is the study. They do link to the studies in the text.

As for controlling for exercise: the whole point of the article is that researchers are finding that outcomes are at least reliably associated (with or without causality) with sedentary activity, that is, specifically measuring the amount of not-doing-anything-physical.

The Warren study very specifically looked at driving and watching TV as it relates to cardiovascular disease. In the introduction, they specifically address your contention:

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Sedentary pursuits represent a unique aspect of human behavior and should not be viewed as simply the extreme low end of the physical activity continuum. For example, several studies have demonstrated that excess TV viewing time, independent from overall physical activity levels, is adversely associated with metabolic risk factors (18)

[ed: ref 18 is Hamilton MT, Hamilton DG, Zderic TW. Role of low energy expenditure and sitting in obesity, metabolic syndrome, type 2 diabetes, and cardiovascular disease. Diabetes. 2007;56(11):2655–67.]

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[carbocation]

I've written to NPR previously about errors that I've found in their presentation of clinical trials and invariably they respond with, "Well, this is our interpretation." Nevermind that said interpretation would get them laughed off of the wards at any teaching hospital. Not saying that about the current article--merely pointing out that even NPR gets it egregiously wrong sometimes.

[bsgreenb]

Even controlling for exercize wouldn't save this study.. Genetic and environmental factors will correlate with a sit-down lifestyle, confounding any possible conclusions.

You could rule out genetic and family environment factors by comparing identical twins who have different sitting habits. My bet is that a big chunk, if not all, of the effect here could be explained by that. For the remaining "effect", you'd still have the issue of non-family environmental collinearity, though.

Maybe you could find a job where people were randomly assigned to sitting vs. standing tasks. That'd be a nifty little natural experiment

[orofino]

Couldn't the same be said of most medical findings? Should we verify all findings utilizing fully controlled testing on twins?

[bsgreenb]

A twin study is just one form of (natural) experiment. It's common in medicine/epidemiology to perform double-blind trials with placebos, etc. Good medical research utilizes experiments rather than assuming causation from correlation like this study does.

I am a big fan of twin studies, though (my background is in behavior genetics). Take the example of smoking. The most solid demonstration that smoking was bad for your health (aside from maybe the experiments on other mammals) was comparison of twins where one twin smoked and the other didn't.

[nostromo]

Well, at least NPR links to the studies they are citing -- so if you really want to dig in to the details, they are right there for you.