Question

8.         Recently a group of adults who swim regularly for exercise were evaluated for depression. It turned out that these swimmers were less likely to be depressed than the general population. The researchers said that the difference was statistically significant.

a.         What does “statistically significant” mean in this context?

b.        Is this an experiment or an observational study? Explain.

c.        News reports claimed this study proved that swimming can prevent depression. Explain why this conclusion is not justified by the study. Include an example of a possible lurking variable.

Answer 1

A.

Statistical significance means that the difference is not due to chance alone and independent variable like "Swimming" also makes a contribution to the difference.

B.

Observational study as we don't inject treatment to a subject, we just performed analysis on certain people who were swimming voluntarily.

C.

Statistical test imply correlation and not causation because there may be confounding variable which may be causing the observed relationship e..g. in this case "Higher testosterone level" in adults induce activities like "swimming" and also inhibits depression.

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