CCDM Statistical Analysis 3 — Questions and Answers
Question 1: What is the primary purpose of stratified randomization in a clinical trial?
- To increase the sample size
- To ensure balance of key prognostic factors across treatment groups (Correct answer)
- To eliminate the need for statistical adjustment
- To reduce the number of protocol deviations
Correct answer: To ensure balance of key prognostic factors across treatment groups
Stratified randomization ensures that important prognostic variables are balanced between treatment arms, reducing confounding.
Question 2: A Type II error (beta error) in hypothesis testing refers to:
- Rejecting the null hypothesis when it is actually true
- Failing to reject the null hypothesis when it is actually false (Correct answer)
- Setting alpha at an incorrect threshold
- Using the wrong statistical test
Correct answer: Failing to reject the null hypothesis when it is actually false
A Type II error (false negative) occurs when a study fails to detect a true treatment effect that actually exists.
Question 3: Which imputation method for missing data assumes data are Missing at Random (MAR) and uses all available data to estimate missing values?
- Last observation carried forward (LOCF)
- Complete case analysis
- Multiple imputation (Correct answer)
- Worst-case imputation
Correct answer: Multiple imputation
Multiple imputation creates several plausible datasets under the MAR assumption, analyzes each, and pools results using Rubin's rules.
Question 4: The Bonferroni correction for multiple comparisons adjusts the significance threshold by:
- Multiplying alpha by the number of comparisons
- Dividing alpha by the number of comparisons (Correct answer)
- Squaring alpha for each additional comparison
- Applying a logarithmic transformation to alpha
Correct answer: Dividing alpha by the number of comparisons
The Bonferroni correction divides the family-wise alpha level by the number of tests to control the overall Type I error rate.
Question 5: What does NNT (Number Needed to Treat) measure in clinical research?
- The number of patients who must be screened to enroll one eligible participant
- The number of patients who must be treated to prevent one additional adverse outcome (Correct answer)
- The ratio of responders in the treatment versus control group
- The minimum sample size required for statistical significance
Correct answer: The number of patients who must be treated to prevent one additional adverse outcome
NNT is the reciprocal of the absolute risk reduction and quantifies the clinical impact of a treatment in practical terms.
Question 6: In a dose-response study, which statistical model is most appropriate for evaluating a monotonic relationship between dose and a continuous outcome?
- Logistic regression
- Linear trend test or regression (Correct answer)
- Chi-square test for independence
- Kaplan-Meier estimation
Correct answer: Linear trend test or regression
A linear trend test or regression analysis evaluates whether increasing dose is associated with a consistent directional change in a continuous outcome.
Question 7: Which term describes the situation where the effect of treatment differs significantly across subgroups of patients?
- Confounding
- Effect modification (interaction) (Correct answer)
- Multicollinearity
- Heteroscedasticity
Correct answer: Effect modification (interaction)
Effect modification, or statistical interaction, occurs when treatment efficacy varies by the level of another variable such as age or disease severity.
CCDM Statistical Analysis 3
What is the primary purpose of stratified randomization in a clinical trial?