It Ain’t Necessarily So
A recent study showing a correlation between vigorous exercise and long life is being hyped by the press as showing that exercise leads to longevity. Michael Eades of Protein Power fame has some worthwhile comments and urges us to remember that correlation does not equal causation.
The conclusion of this study, which is absolutely accurate, is that running is associated with longevity and reduced disability. The two are associated or correlated. The study does not prove that running increases longevity or decreases disability. Correlation is not causation.
But you wouldn’t know that from the press coverage of this study. If you run a Google search, you will find the study reported as proving causality. See here, here and here for just a few instances.
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We don’t know and can’t possibly determine from this study whether it is the running that increases longevity or whether there is some facet of personality or physiology that drives one to run that increases longevity. Maybe people who are destined to live longer take to running or other forms or aerobic exercise. People who are depressed typically have shorter lives, and people who are depressed tend not to join groups or exercise. Perhaps a number of the people in the control group are depressed, leading to an increase in early deaths in that group. It could be that the people who have the time to join a running group and spend the time running are more financially stable and are happier. Both of those conditions are correlated with longevity. There are far too many factors separating the two groups to dissect out the one and attach the benefit to it. But our culture firmly believes that exercise promotes longevity, so this experiment seems to bear that out, and most people accept it without looking to deeply.
Good stuff.
