CPI Study Design & Methodology 3 — Questions and Answers
Question 1: A PI wants to minimize selection bias in a clinical trial. Which allocation method is most effective?
- Alternate assignment
- Investigator judgment
- Concealed randomization (Correct answer)
- Volunteer-based selection
Correct answer: Concealed randomization
Concealed randomization (allocation concealment) prevents investigators from predicting or influencing group assignments, minimizing selection bias.
Question 2: In a dose-response study, what does a monotonic relationship between dose and response indicate?
- The response plateaus at high doses
- The response consistently increases or decreases with dose (Correct answer)
- The response is U-shaped
- The relationship is nonlinear only
Correct answer: The response consistently increases or decreases with dose
A monotonic dose-response relationship means the response consistently moves in one direction (up or down) as the dose increases, supporting causality.
Question 3: Which term describes the ability of a study to detect a true effect when one exists?
- Specificity
- Sensitivity
- Statistical power (Correct answer)
- Positive predictive value
Correct answer: Statistical power
Statistical power (1-β) is the probability of correctly rejecting a false null hypothesis, i.e., detecting a real effect.
Question 4: A researcher uses historical medical records to follow patients forward in time from exposure to outcome. This is a:
- Retrospective case-control study
- Ambidirectional cohort study
- Historical prospective cohort study (Correct answer)
- Nested case-control study
Correct answer: Historical prospective cohort study
A historical prospective cohort study uses existing records to reconstruct cohort exposure and then tracks outcomes forward in time.
Question 5: When calculating sample size for a clinical trial, increasing the desired power from 80% to 90% will:
- Decrease required sample size
- Increase required sample size (Correct answer)
- Have no effect on sample size
- Only affect allocation ratio
Correct answer: Increase required sample size
Higher power requires detecting smaller or less likely effects, necessitating a larger sample to achieve that statistical certainty.
Question 6: A study designed to detect a clinically meaningful difference of 5 mmHg in blood pressure uses 80% power and α=0.05. If the true effect is 3 mmHg, the study is likely to:
- Correctly reject H0
- Commit a Type I error
- Commit a Type II error (Correct answer)
- Have inflated power
Correct answer: Commit a Type II error
When the true effect is smaller than the detectable difference the study was powered for, it is underpowered and likely to miss the effect (Type II error).
Question 7: Equipoise in clinical research means that:
- All participants receive equal doses
- Genuine uncertainty exists about which treatment is superior (Correct answer)
- The study arms are equal in size
- Data are balanced across sites
Correct answer: Genuine uncertainty exists about which treatment is superior
Clinical equipoise refers to genuine uncertainty in the medical community about which treatment is better, ethically justifying a randomized trial.
CPI Study Design & Methodology 3
A PI wants to minimize selection bias in a clinical trial.
Which allocation method is most effective?