I was surprised to see in Science News, conclusions about causation made on the basis of correlational research. The variance in activity levels may have been a consequence of differing levels of energy among the participants at the outset of the study, perhaps due to differences in general health. We should be careful about this victim-blaming habit.

Joan Sophie
Chicago, Ill.

Perhaps the more sedentary people in the study had underlying medical problems that caused them to lack energy and to die earlier than the active people. In an effort to address that issue, the study authors accounted for many factors, such as body fat, race, heart disease, diabetes, cancer, and smoking status, in the study participants. —N. Seppa

From the Nature Index

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