MJDF Dental Public Health & Evidence-Based Dentistry 2 — Questions and Answers
Question 1: What is a systematic review in the hierarchy of evidence?
- A rigorous synthesis of all available evidence on a defined question using pre-specified methods, typically including meta-analysis — highest quality evidence for clinical decisions (Correct answer)
- A narrative review by an expert
- A single randomised controlled trial
- A cross-sectional survey
Correct answer: A rigorous synthesis of all available evidence on a defined question using pre-specified methods, typically including meta-analysis — highest quality evidence for clinical decisions
Systematic reviews use transparent, reproducible methodology to identify, appraise, and synthesise evidence from all relevant studies on a clinical question, reducing bias; meta-analysis statistically pools data when appropriate.
Question 2: What is the difference between relative risk reduction (RRR) and absolute risk reduction (ARR)?
- RRR is the proportional reduction in risk; ARR is the absolute difference in event rates between groups — ARR is clinically more meaningful (Correct answer)
- They are identical
- RRR is always larger and more clinically meaningful
- ARR is a percentage; RRR is absolute
Correct answer: RRR is the proportional reduction in risk; ARR is the absolute difference in event rates between groups — ARR is clinically more meaningful
ARR is the actual difference in risk (e.g., 2% vs. 1% = 1% ARR); RRR expresses this as a proportion of the control group risk (e.g., 50% RRR). ARR is more clinically meaningful — a 50% RRR with a very small ARR may not justify treatment.
Question 3: What is 'number needed to treat' (NNT) in evidence-based dentistry?
- Reciprocal of ARR — how many patients must be treated to prevent one additional event; lower NNT = more effective treatment (Correct answer)
- The number of trials needed to recommend a treatment
- The number of times a treatment must be repeated
- The number of patients in a study
Correct answer: Reciprocal of ARR — how many patients must be treated to prevent one additional event; lower NNT = more effective treatment
NNT = 1/ARR; if ARR is 10% (0.10), NNT = 10 — you treat 10 patients to prevent one adverse outcome. NNT is a practical measure of treatment effectiveness in clinical decision-making.
Question 4: What is 'publication bias' in the context of systematic reviews?
- The tendency for positive studies to be published more readily than negative studies, skewing systematic review conclusions towards overestimated treatment effects (Correct answer)
- The bias introduced by reviewer preferences
- The tendency to reject poor-quality trials
- Bias caused by industry funding
Correct answer: The tendency for positive studies to be published more readily than negative studies, skewing systematic review conclusions towards overestimated treatment effects
Publication bias occurs because studies showing positive results are more likely to be published; negative or null results remain unpublished, causing systematic reviews to overestimate treatment benefits.
Question 5: What is the Bradford Hill criterion of 'biological plausibility' in epidemiological causal inference?
- A plausible mechanism exists by which the exposure could cause the outcome — supports but does not prove causality (Correct answer)
- The strongest single criterion for causation
- Equivalent to statistical significance
- Only required for infectious disease research
Correct answer: A plausible mechanism exists by which the exposure could cause the outcome — supports but does not prove causality
Biological plausibility means there is a known or hypothesised mechanism that could explain the exposure-outcome relationship; it is one of Hill's nine criteria for assessing causality but is not sufficient alone.
Question 6: What is the most appropriate study design to determine the prevalence of dental caries in a population?
- Cross-sectional epidemiological survey (Correct answer)
- Randomised controlled trial
- Case-control study
- Longitudinal cohort study
Correct answer: Cross-sectional epidemiological survey
Cross-sectional surveys measure the prevalence of disease at a single point in time across a population, making them ideal for descriptive epidemiology of conditions like dental caries at the population level.
MJDF Dental Public Health & Evidence-Based Dentistry 2
What is a systematic review in the hierarchy of evidence?