Research & Evidence-Based Medicine

20 learning units • 100 chapter sections • 200 explained questions. Build a question, judge the evidence and connect the answer with the person receiving care.

Original RAHBAR study material for the Year 3 learning pathway. Educational examples support supervised learning; institutional research and clinical requirements still apply. References & further reading ↓

MODULE 11 / 20

Bias, Confounding & Causal Reasoning

Identify systematic distortions and distinguish a confounder from a mediator or an effect modifier.

Answer all 10 questions, then submit to see your score and explanations. This is a self-study exercise; results are not saved.

Question 01. Sicker patients preferentially receive a drug and have higher mortality. What is a key concern? A. Confounding by indicationB. Perfect randomisationC. Purely random measurement noise onlyD. Guaranteed drug toxicity

Question 02. Which problem is not automatically solved by increasing sample size? A. Sampling imprecision under a fixed valid designB. Standard error from independent observationsC. Random fluctuation in a sample meanD. Systematic bias

Question 03. What is a mediator? A. Any variable with a large p-valueB. The trial registration numberC. A variable on the causal path from exposure to outcomeD. A variable that cannot be measured

Question 04. What can conditioning on a collider do? A. Always remove every confounderB. Guarantee unbiased predictionC. Introduce a spurious associationD. Make all exposures randomised

Question 05. What is effect modification? A. Every observed difference is measurement errorB. A synonym for non-responseC. An effect differs across levels of another factor on a specified scaleD. A guarantee of publication bias

Question 06. How should regression adjustment variables be chosen for causal estimation? A. Using causal knowledge and the target effectB. Only by selecting every small p-valueC. By including all post-treatment variables automaticallyD. By choosing those that maximise significance

Question 07. Can regression guarantee removal of confounding? A. No, unmeasured or poorly measured factors may remainB. Yes, any model removes all confoundingC. Yes, if there are many decimalsD. Only journal formatting matters

Question 08. Which comparison is most vulnerable to recall bias? A. Blinded automated measurement with complete recordsB. A concealed random allocation sequenceC. A prespecified sample-size calculationD. Cases and controls recalling past exposure differently

Question 09. Why can adjusting for a mediator be inappropriate for a total-effect question? A. It may remove part of the effect being estimatedB. It always increases the true total effectC. Mediators are always random sampling errorsD. It guarantees external validity

Question 10. What is the strongest response to an observational association? A. Declare causation from the p-value aloneB. Ignore the comparison groupC. Evaluate temporality, confounding and alternative explanationsD. Treat correlation as random assignment

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References & Further Reading

Use the full methods and relevant chapters when appraising a paper. These sources support further study; the examples and questions above are original teaching exercises.

Reference review: 25 September 2026. Consult current institutional guidance for project approval and clinical decisions.