General Surgery Board Review Research & Evidence-Based Practice 3 — Questions and Answers
Question 1: A prospective cohort study follows 500 smokers and 500 non-smokers for 10 years to assess colorectal cancer risk. What is the best measure of association to report?
- Odds ratio
- Relative risk (Correct answer)
- Attributable risk percent
- Number needed to harm
Correct answer: Relative risk
Relative risk (risk ratio) is the appropriate measure of association for cohort studies because incidence can be calculated directly.
Question 2: Publication bias in surgical literature most commonly results in:
- Overrepresentation of negative trials
- Overestimation of intervention benefits (Correct answer)
- Underreporting of adverse events in positive trials
- Equal representation of all study outcomes
Correct answer: Overestimation of intervention benefits
Publication bias leads to overestimation of treatment benefits because positive trials are more likely to be published than negative ones.
Question 3: Which of the following best defines 'internal validity' of a clinical trial?
- The degree to which results can be generalized to other populations
- The accuracy with which the study measures what it intends to within its own sample (Correct answer)
- The statistical power to detect a true effect
- The reproducibility of results across multiple institutions
Correct answer: The accuracy with which the study measures what it intends to within its own sample
Internal validity refers to how well a study accurately measures the causal relationship within its specific study population.
Question 4: In a surgical RCT, 'intention-to-treat' (ITT) analysis means:
- Analyzing only patients who completed the protocol
- Analyzing all randomized patients in their originally assigned groups regardless of what they received (Correct answer)
- Excluding patients who crossed over to the other arm
- Including only patients who were compliant with treatment
Correct answer: Analyzing all randomized patients in their originally assigned groups regardless of what they received
ITT analysis preserves randomization by analyzing patients in their allocated groups regardless of protocol adherence or crossover.
Question 5: Sensitivity of a diagnostic test is best defined as the probability that:
- A positive test result is truly positive
- The test is positive given that disease is present (Correct answer)
- The test is negative given that disease is absent
- A negative result rules out disease in a high-risk patient
Correct answer: The test is positive given that disease is present
Sensitivity = TP / (TP + FN); it measures how well the test identifies patients who truly have the disease.
Question 6: When evaluating evidence for adopting a new surgical technique, which GRADE rating indicates the highest certainty of evidence?
- Very low
- Low
- Moderate
- High (Correct answer)
Correct answer: High
The GRADE system rates evidence quality as Very Low, Low, Moderate, or High; High indicates the greatest confidence in the effect estimate.
Question 7: A case-control study investigating anastomotic leak after colorectal surgery would most appropriately select controls as:
- Patients who underwent the same surgery without anastomotic leak (Correct answer)
- Healthy volunteers matched for age and sex
- Patients from a different hospital with similar demographics
- Patients with other types of surgical complications
Correct answer: Patients who underwent the same surgery without anastomotic leak
Controls in surgical case-control studies should be drawn from the same source population as cases, ideally patients who underwent the same procedure without the outcome of interest.
General Surgery Board Review Research & Evidence-Based Practice 3
A prospective cohort study follows 500 smokers and 500 non-smokers for 10 years to assess colorectal cancer risk.
What is the best measure of association to report?