Connor conducts research to find out if regular exercise improves students’ lung function. However, Connor does NOT keep track of which students smoke and which don’t. Whether a student smokes is likely to be a what in this study?

Whether students smoke could affect lung function, independently of how much they exercise. Since Connor does not track smoking, differences in smoking could influence the results and make it harder to tell whether exercise caused any improvement. Smoking is therefore a confounding variable.

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