50 minutes. Self-marked. 12 marks. Write your answers, open the model answer, then tick each mark you earned honestly. Nothing is sent or stored.
Scenario (invented)
An app advertises: “Find your purpose and cut your risk of a heart attack by 17% — proven by science!” The advert cites a review reporting a relative risk of 0.83 (95% CI 0.75 to 0.92) for cardiovascular events among people with a high sense of purpose.
Task 1 (2 marks)
Show how 17% is obtained and compute the absolute risk if the comparison group’s risk is 12%.
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Task 2 (3 marks)
Explain in plain language what the interval tells you.
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Task 3 (3 marks)
Give three problems with the advert.
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Task 4 (4 marks)
Write the five-line evidence card for “high purpose is associated with lower risk”, and write one testable prediction from self-determination theory that the app could be tested on.
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Rubric and model answer
Task 1 (2 marks)
(1 − 0.83) × 100 = 17% relative reduction. Absolute risk = 0.83 × 12% = about 10% (9.96%), a difference of about 2 percentage points.
Task 2 (3 marks)
The interval 0.75 to 0.92 lies below 1, so no association is incompatible with the data, and the true relative risk could plausibly be anywhere in that range, from about 8% to 25% lower.
Task 3 (3 marks)
Any three: “proven” is too strong; observational studies cannot rule out reverse causation or a third factor; the review compares people who have purpose with those who do not, but does not show that an app creates purpose; 17% is relative, not absolute; the average hides individuals; the advert sells a product.
Task 4 (4 marks)
Claim: high purpose is associated with lower mortality and cardiovascular risk. Mechanism (proposed): healthier behaviour and stress responses. Best evidence: 10 prospective studies, 136,265 participants, RR 0.83. Strength: Moderate for association, Low for cause. Limits: observational; direction of cause open. Prediction: users who choose their own goals in the app (autonomy) will keep using it longer than users assigned goals.
Marks so far: 0 of 12