A study finds that coffee drinkers have more lung cancer than non-drinkers. Many coffee drinkers also smoke. What is smoking in this relationship?
Answer and explanation
Correct answer: A. A confounder
- Step 1: A confounder is associated with both exposure and outcome and is not on the causal pathway.
- Step 2: Smoking is linked to coffee drinking and independently causes lung cancer, producing a spurious association.
Answer
A confounder.
Why not the others: A mediator that lies on the causal pathway between coffee and cancer: A mediator lies between exposure and outcome, which smoking does not. A source of random error that will disappear in a larger sample: Random error is chance variation, not a systematic third factor. An effect modifier only: Effect modification means the effect differs by level of a variable.
Practise more More statistics and appraisal.
Free questions with an explanation for every one, and full timed PLAB 1 (GMC, international medical graduates) mock tests.
More More statistics and appraisal questions
- In a cohort followed for 15 000 person-years, 45 people developed a new diagnosis of type 2 diabetes. What is the incidence rate?
- A chronic disease has an incidence of 2 per 1000 per year and an average duration of 5 years, in a stable population. What is its approximat…
- A trial reports that 5 percent of patients on a drug and 2 percent on placebo had a serious adverse event. What is the number needed to harm…
- In a trial the event rate was 25 percent in the control group and 15 percent in the treatment group. What is the relative risk reduction?
- Which of the following is at the top of the hierarchy of evidence for the effectiveness of a treatment?
- A very sensitive test is negative in a patient. What can be said?