General Surgery Board Review Research & Evidence-Based Practice 2 — Questions and Answers
Question 1: In a randomized controlled trial, what is the primary purpose of allocation concealment?
- To blind participants to their treatment assignment
- To prevent selection bias during randomization (Correct answer)
- To ensure equal group sizes at baseline
- To reduce attrition during follow-up
Correct answer: To prevent selection bias during randomization
Allocation concealment prevents those enrolling patients from knowing the upcoming assignment, which eliminates selection bias during randomization.
Question 2: A surgeon reads a meta-analysis reporting a pooled odds ratio of 1.8 (95% CI: 0.9–3.6) for wound infection after laparoscopic vs. open appendectomy. What is the correct interpretation?
- Laparoscopic surgery significantly increases wound infection risk
- The result is statistically significant because OR > 1
- The confidence interval crosses 1, so the result is not statistically significant (Correct answer)
- The study is underpowered and should be ignored
Correct answer: The confidence interval crosses 1, so the result is not statistically significant
A 95% CI that crosses 1.0 means the result is not statistically significant at the 0.05 level.
Question 3: Which study design provides the highest level of evidence for evaluating a surgical intervention?
- Prospective cohort study
- Case-control study
- Systematic review of randomized controlled trials (Correct answer)
- Expert consensus guidelines
Correct answer: Systematic review of randomized controlled trials
Systematic reviews and meta-analyses of RCTs sit at the top of the evidence hierarchy (Level I evidence).
Question 4: The number needed to treat (NNT) is calculated as:
- 1 / relative risk reduction
- 1 / absolute risk reduction (Correct answer)
- Relative risk / absolute risk reduction
- Odds ratio / (1 − odds ratio)
Correct answer: 1 / absolute risk reduction
NNT = 1 / ARR (absolute risk reduction), which indicates how many patients must be treated to prevent one additional bad outcome.
Question 5: A clinical trial reports P = 0.04 with a clinically trivial effect size. What is the most appropriate conclusion?
- The intervention is clinically meaningful because P < 0.05
- Statistical significance does not imply clinical significance (Correct answer)
- The trial should be repeated with a larger sample
- The effect size should be disregarded in favor of the P value
Correct answer: Statistical significance does not imply clinical significance
A statistically significant P value with a trivial effect size indicates the finding may not be clinically meaningful.
Question 6: Which bias occurs when patients who are lost to follow-up differ systematically from those who complete a study?
- Recall bias
- Attrition bias (Correct answer)
- Detection bias
- Confounding
Correct answer: Attrition bias
Attrition bias arises when dropouts differ from completers in ways that affect the outcome, skewing results.
Question 7: In evidence-based surgery, a 'forest plot' in a meta-analysis is used to:
- Display the geographic distribution of study sites
- Illustrate individual study effect estimates and the pooled result (Correct answer)
- Map the surgical anatomy referenced in included studies
- Show the timeline of publication dates for included trials
Correct answer: Illustrate individual study effect estimates and the pooled result
A forest plot graphically displays each study's effect estimate with confidence intervals and the overall pooled estimate.
General Surgery Board Review Research & Evidence-Based Practice 2
In a randomized controlled trial, what is the primary purpose of allocation concealment?