FPGEE Biostatistics 2 — Questions and Answers
Question 1: A clinical trial reports a 95% confidence interval for the difference in mean blood pressure reduction as (2.1, 8.4 mmHg). Which conclusion is most appropriate?
- The true difference is exactly 5.25 mmHg
- We are 95% confident the true difference lies between 2.1 and 8.4 mmHg (Correct answer)
- There is a 95% probability the null hypothesis is false
- The p-value is 0.95
Correct answer: We are 95% confident the true difference lies between 2.1 and 8.4 mmHg
A 95% CI means that 95% of such intervals constructed from repeated sampling would contain the true population parameter.
Question 2: In a study, the Number Needed to Treat (NNT) is calculated as 8. What does this mean?
- 8% of patients will respond to treatment
- 8 patients must be treated for one additional patient to benefit (Correct answer)
- The treatment reduces risk by 8%
- 8 patients experienced adverse events
Correct answer: 8 patients must be treated for one additional patient to benefit
NNT is the reciprocal of the absolute risk reduction and represents how many patients need treatment for one additional benefit.
Question 3: Which type of bias occurs when patients who drop out of a clinical trial differ systematically from those who complete it?
- Selection bias
- Information bias
- Attrition bias (Correct answer)
- Confounding bias
Correct answer: Attrition bias
Attrition bias (also called dropout bias) occurs when loss to follow-up is related to the outcome, distorting results.
Question 4: A study finds r = 0.85 between drug dose and therapeutic response. What does this Pearson correlation coefficient indicate?
- Drug dose causes an 85% improvement in response
- There is a strong positive linear relationship between dose and response (Correct answer)
- 85% of patients responded to the drug
- The regression slope is 0.85
Correct answer: There is a strong positive linear relationship between dose and response
A Pearson r of 0.85 indicates a strong positive linear association, but does not imply causation.
Question 5: A researcher increases sample size from 100 to 400. How does this affect the standard error of the mean?
- It doubles
- It is halved (Correct answer)
- It is quartered
- It remains the same
Correct answer: It is halved
Standard error = SD/√n; quadrupling n doubles √n, so the SE is halved.
Question 6: In a 2×2 contingency table used for a case-control study, which measure of association is most appropriate?
- Relative risk
- Odds ratio (Correct answer)
- Attributable risk
- Hazard ratio
Correct answer: Odds ratio
In case-control studies, disease incidence cannot be directly calculated, so the odds ratio is the appropriate measure of association.
Question 7: A pharmacokinetic study shows a drug's half-life follows a log-normal distribution. What transformation would make it approximately normal?
- Square root transformation
- Log transformation (Correct answer)
- Reciprocal transformation
- Z-score standardization
Correct answer: Log transformation
A log transformation converts a log-normal distribution to a normal distribution, enabling parametric statistical analyses.
FPGEE Biostatistics 2
A clinical trial reports a 95% confidence interval for the difference in mean blood pressure reduction as (2.1, 8.4 mmHg).
Which conclusion is most appropriate?