ACRP ACRP Biostatistics and Data Analysis 1 — Questions and Answers
Question 1: What is the purpose of calculating sample size before initiating a clinical trial?
- To determine budget allocation
- To ensure the study has sufficient statistical power to detect a clinically meaningful difference (Correct answer)
- To satisfy sponsor marketing requirements
- To limit participant enrollment costs
Correct answer: To ensure the study has sufficient statistical power to detect a clinically meaningful difference
Sample size calculations ensure the trial is adequately powered to detect the pre-specified effect size with acceptable type I and type II error rates.
Question 2: What does 'statistical power' mean in a clinical trial?
- The computing power of the statistical software used
- The probability of correctly rejecting a false null hypothesis (Correct answer)
- The number of statistical tests performed
- The strength of the treatment effect
Correct answer: The probability of correctly rejecting a false null hypothesis
Statistical power (1 − β) is the probability that a study will detect a true treatment effect when one actually exists.
Question 3: What is a p-value in the context of clinical trial results?
- The probability that the study drug is effective
- The probability of observing results as extreme as those found, assuming the null hypothesis is true (Correct answer)
- The percentage of participants who responded to treatment
- The power of the statistical test used
Correct answer: The probability of observing results as extreme as those found, assuming the null hypothesis is true
A p-value quantifies how likely the observed data would occur by chance if the null hypothesis were true; it does not measure effect size or clinical significance.
Question 4: What is the difference between per-protocol (PP) and intent-to-treat (ITT) analysis in clinical trials?
- PP includes all enrolled participants; ITT includes only completers
- ITT includes all randomized participants regardless of compliance; PP includes only those who completed per protocol (Correct answer)
- Both methods are identical in practice
- PP is used for safety analysis; ITT is used for efficacy only
Correct answer: ITT includes all randomized participants regardless of compliance; PP includes only those who completed per protocol
ITT preserves randomization by analyzing all participants as randomized, while PP analysis is restricted to those who adhered to the protocol, which may introduce bias.
Question 5: What is randomization in clinical trials and why is it important?
- Randomly selecting study sites for enrollment
- Randomly assigning participants to treatment groups to eliminate selection bias and balance confounders (Correct answer)
- Randomly choosing the primary endpoint
- Randomly ordering case report form questions
Correct answer: Randomly assigning participants to treatment groups to eliminate selection bias and balance confounders
Randomization distributes known and unknown confounding variables equally across treatment groups, ensuring valid comparison of outcomes.
Question 6: What is a confidence interval (CI) and how is it interpreted in clinical trial results?
- A range indicating participant age distribution
- A range of values within which the true population parameter is estimated to lie with a specified probability (Correct answer)
- The margin of error in data entry
- The sponsor's confidence in the trial outcome
Correct answer: A range of values within which the true population parameter is estimated to lie with a specified probability
A 95% CI means that if the study were repeated 100 times, the true effect would fall within the calculated interval approximately 95 times.
ACRP ACRP Biostatistics and Data Analysis 1
What is the purpose of calculating sample size before initiating a clinical trial?