BMAT Research & Evidence-Based Practice 5 — Questions and Answers
Question 1: Recall bias is most likely to affect which type of study?
- Prospective cohort study
- Randomized controlled trial
- Case-control study (Correct answer)
- Cross-sectional survey of objective measurements
Correct answer: Case-control study
In case-control studies, cases may recall past exposures differently than controls, systematically distorting the exposure-outcome relationship.
Question 2: A study reports relative risk reduction (RRR) of 50% for a treatment. The baseline risk is 2%. What is the absolute risk reduction (ARR)?
- 50%
- 2%
- 1% (Correct answer)
- 48%
Correct answer: 1%
ARR = RRR × baseline risk = 0.50 × 0.02 = 0.01 (1%), illustrating why absolute measures are often more clinically meaningful.
Question 3: Which of the following best describes 'external validity' (generalizability) of a study?
- The degree to which the study correctly measures the intended variable
- The extent to which study findings can be applied to populations beyond the study sample (Correct answer)
- The probability that results are due to chance
- The consistency of results across repeated measurements
Correct answer: The extent to which study findings can be applied to populations beyond the study sample
External validity refers to how well study results can be generalized to other populations, settings, or time periods.
Question 4: In a randomized controlled trial, double-blinding is used to prevent:
- Selection bias and performance bias simultaneously
- Attrition bias and reporting bias
- Both performance bias (participant behavior) and detection bias (outcome assessment) (Correct answer)
- Confounding and ecological fallacy
Correct answer: Both performance bias (participant behavior) and detection bias (outcome assessment)
Double-blinding hides treatment allocation from both participants (preventing performance bias) and assessors (preventing detection bias).
Question 5: A systematic review differs from a narrative review primarily because it:
- Is written by more authors
- Uses predefined search strategies and explicit inclusion/exclusion criteria to minimize bias (Correct answer)
- Focuses on more recent literature
- Requires a minimum of 20 included studies
Correct answer: Uses predefined search strategies and explicit inclusion/exclusion criteria to minimize bias
Systematic reviews follow a transparent, reproducible protocol with defined methods, reducing the selective inclusion bias common in narrative reviews.
Question 6: Which of the following is the most appropriate measure of association in a cohort study?
- Odds ratio
- Relative risk (risk ratio) (Correct answer)
- Prevalence ratio
- Attributable fraction
Correct answer: Relative risk (risk ratio)
Because cohort studies directly measure incidence in exposed and unexposed groups, relative risk (risk ratio) is the natural measure of association.
Question 7: The concept of 'number needed to harm' (NNH) is most useful for:
- Determining the efficacy of a treatment compared to placebo
- Communicating the risk of adverse effects to patients and clinicians (Correct answer)
- Calculating the cost-effectiveness of an intervention
- Estimating the sample size required for a clinical trial
Correct answer: Communicating the risk of adverse effects to patients and clinicians
NNH quantifies how many patients must be exposed to a treatment before one additional patient experiences harm, aiding risk communication.
BMAT Research & Evidence-Based Practice 5
Recall bias is most likely to affect which type of study?