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Medical Ethics, Consent & Evidence-Based Medicine Flashcards

6 cards from real PLAB 1 practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. A clinical trial reports that a new drug reduces the relative risk of myocardial infarction by 50% compared to placebo. The absolute event rates are 2% (treatment) and 4% (control). What is the Number Needed to Treat (NNT)?

    Answer: 50

    NNT = 1 / Absolute Risk Reduction (ARR). ARR = 4% - 2% = 2% = 0.02. NNT = 1/0.02 = 50. The NNT of 50 means you need to treat 50 patients to prevent one MI. While the relative risk reduction (50%) sounds impressive, the NNT provides more clinically meaningful information.

  2. What is a 'double-blind randomised controlled trial' (RCT) and why is it considered the gold standard for establishing therapeutic efficacy?

    Answer: A trial where neither participants nor investigators know which group receives treatment or placebo, eliminating allocation bias and expectation bias — the best evidence for causality

    A double-blind RCT: random allocation prevents selection bias and balances confounders; blinding participants prevents placebo effect; blinding investigators prevents observer bias. The combination of randomisation and blinding provides the most robust evidence for causality in therapeutic research.

  3. What is 'sensitivity' of a diagnostic test?

    Answer: The proportion of people with the disease who test positive (true positive rate) — a sensitive test rarely misses disease

    Sensitivity = True Positives / (True Positives + False Negatives). A highly sensitive test has a low false-negative rate — it rarely misses cases of the disease. Mnemonic: SnNout — a Sensitive test, when Negative, rules OUT disease. Useful for screening tests.

  4. What is 'specificity' of a diagnostic test?

    Answer: The proportion of disease-free individuals who test negative (true negative rate) — a specific test rarely gives false positives

    Specificity = True Negatives / (True Negatives + False Positives). A highly specific test rarely gives a positive result in people without disease. Mnemonic: SpPin — a Specific test, when Positive, rules IN disease. Useful for confirmatory tests.

  5. What does 'intention-to-treat' (ITT) analysis mean in clinical trials?

    Answer: Analysis that includes all participants as originally allocated, regardless of whether they completed or received the allocated treatment — preserving the integrity of randomisation

    ITT analysis maintains all participants in the groups to which they were originally randomised, regardless of non-compliance, withdrawal, or crossover. This preserves the prognostic balance of randomisation and gives a real-world estimate of treatment effect. Per-protocol analysis (completers only) may overestimate treatment benefit.

  6. What does a 'confidence interval' (CI) tell you in clinical research?

    Answer: The range within which the true population value is likely to lie with a specified probability (e.g., 95% CI) — a wide CI indicates less precision

    A 95% CI means that if the study were repeated 100 times, 95 of the resulting CIs would contain the true population value. A wide CI reflects high uncertainty (often from small sample size); a narrow CI indicates precision. If a CI for a risk ratio includes 1.0, the result is not statistically significant at the 5% level.