Which conclusion is best supported by this study?

Question

Researchers recorded the eating habits of 500 volunteers for one year. They did not assign anyone to a diet. Volunteers who regularly ate breakfast had a lower average body mass index than those who regularly skipped it.

Accepted Answer

A. Among these volunteers, regularly eating breakfast is associated with a lower average body mass index.. The researchers observed what volunteers already did rather than assigning them to eat or skip breakfast. An observational study like this can establish that two things go together in the group studied, but not that one produced the other.

Answer

B. Regularly eating breakfast causes a lower body mass index. — Without random assignment, the breakfast eaters may differ from the skippers in other ways — sleep, exercise, income — and any of those could explain the gap. The study shows a link, not a cause.

Answer

C. Skipping breakfast causes a higher body mass index. — This is the same causal leap as B, just pointed the other way. The design can't support a cause in either direction.

Answer

D. Eating breakfast has no effect on body mass index. — The study found a difference between the groups, so 'no effect' contradicts the data. It simply can't tell us whether the effect is causal.

Problem-Solving and Data Analysis practice question

Answer: A. Among these volunteers, regularly eating breakfast is associated with a lower average body mass index.

Why the other answers are wrong

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