Pupils who chose to attend an optional after-school maths club scored higher on average on the end-of-year exam than pupils who did not attend. A teacher concludes that the club causes higher scores. Which of the following is the strongest reason the conclusion is not justified?

Question

Accepted Answer

A. Pupils chose whether to attend, so those who were already stronger or more motivated in maths may have been more likely to join.. Self-selection means attendance is confounded with prior ability and motivation; only random assignment would support a causal claim.

Answer

B. The exam was taken at the end of the year rather than the start. — Timing of the exam does not create the confounding.

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C. The club met after school rather than during the school day. — When the club met is irrelevant to the inference.

Answer

D. The average score was used instead of the median. — The choice of average does not address causation.

Problem-Solving and Data Analysis practice question

Answer: A. Pupils chose whether to attend, so those who were already stronger or more motivated in maths may have been more likely to join.

Why the other answers are wrong

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