CTA CTA Biostatistics & Study Design 2 — Questions and Answers
Question 1: What is statistical power in a clinical trial?
- The probability of making a Type I error
- The probability of correctly detecting a true treatment effect (Correct answer)
- The sample size needed for a study
- The level of statistical significance chosen
Correct answer: The probability of correctly detecting a true treatment effect
Statistical power is the probability that a study will detect a true treatment effect when one actually exists, often set at 80% or higher.
Question 2: In clinical trials, what does a p-value of less than 0.05 typically indicate?
- The study had sufficient sample size
- The result is statistically significant at the 5% level (Correct answer)
- The treatment is clinically meaningful
- The trial was properly blinded
Correct answer: The result is statistically significant at the 5% level
A p-value < 0.05 indicates that the observed result would occur less than 5% of the time by chance alone, meeting the conventional threshold for statistical significance.
Question 3: What is the null hypothesis in a clinical trial?
- The assumption that the new treatment is superior
- The assumption that there is no difference between treatment and control (Correct answer)
- The minimum clinically important difference
- The expected adverse event rate
Correct answer: The assumption that there is no difference between treatment and control
The null hypothesis assumes no difference between the treatment and control groups, and statistical testing is used to determine whether there is sufficient evidence to reject it.
Question 4: What is a confidence interval (CI) used for in clinical trial reporting?
- To determine the optimal dose of a drug
- To express the range within which the true treatment effect likely falls (Correct answer)
- To calculate the required sample size
- To assign participants to treatment groups
Correct answer: To express the range within which the true treatment effect likely falls
A confidence interval provides a range of plausible values for the true treatment effect, with a 95% CI meaning the true value falls within that range 95% of the time.
Question 5: What is randomization stratification used for in a clinical trial?
- To increase the number of participants enrolled
- To ensure balance of key prognostic factors across treatment groups (Correct answer)
- To blind investigators to treatment assignments
- To determine the primary endpoint of the study
Correct answer: To ensure balance of key prognostic factors across treatment groups
Stratified randomization ensures that important prognostic factors (such as age or disease severity) are evenly distributed across treatment groups to reduce confounding.
Question 6: Which analysis population includes all randomized participants regardless of protocol deviations?
- Per-protocol population
- Safety population
- Intent-to-treat (ITT) population (Correct answer)
- Evaluable population
Correct answer: Intent-to-treat (ITT) population
The intent-to-treat (ITT) population includes all randomized participants analyzed in their originally assigned groups, regardless of protocol adherence or withdrawal.
CTA CTA Biostatistics & Study Design 2
What is statistical power in a clinical trial?