The main problem is that sample sizes are large in the "less exercise" groups, which means they have a statistically significant reduction in mortality, but they are tiny in the "more exercise" groups, which means they don't have a statistically significant reduction in mortality. This allows the authors to make the shamefully disingenuous argument that "strenuous joggers have a mortality rate not statistically different from that of the sedentary group"–which is almost a foregone conclusion, given that the sample size is less than a tenth as large.
Does your risk really go up if you run more than 2.5 hours, but then go down again if you run more than four hours? Of course not. These are not real patterns, because we're talking about one, two, three, or at most five or six deaths. No matter how interesting or important the question is, you can't torture these numbers enough to force them to reveal the answers. They're simply not there.Hutchinson points out other statistical challenges with the data including age and gender.
In addition, the study's findings have only to do with mortality during the study period. Many mainstream articles, however, have broadened the conclusion to suggest more ambitious running is of equal health benefit to being sedentary. Such claims ignore the wealth of data that show that, while many of the health benefits of running accrue at modest amounts of mileage, in many studies, higher-mileage runners gain more benefits.The media loves sensational headlines, but I'm going with Runner's World on this one when they conclude that "We at Runner's World don't think this one study is reason to change your approach to or appreciation of running."
Labels: running new