STP Data Analysis 5 — Questions and Answers
Question 1: A study reports a relative risk (RR) of 2.0 with a 95% CI of 1.2–3.5. What can be concluded?
- The result is not statistically significant
- The exposed group has twice the risk, and the result is statistically significant (Correct answer)
- The result is clinically insignificant
- The confidence interval indicates high variability only
Correct answer: The exposed group has twice the risk, and the result is statistically significant
RR = 2.0 means twice the risk in the exposed group; since the 95% CI does not include 1.0, the result is statistically significant.
Question 2: When calculating a non-parametric reference interval using the CLSI C28-A3 method with 120 samples, the 2.5th percentile is determined by:
- The mean minus 1.96 SD
- Ranking data and selecting the 3rd lowest value (Correct answer)
- The value at rank position 0.025 × 120
- Using a log-normal model to back-transform the result
Correct answer: Ranking data and selecting the 3rd lowest value
CLSI C28-A3 ranks the 120 values; the 2.5th percentile is the 3rd lowest value (rank 3 = 0.025 × 120).
Question 3: Which of the following best describes a Type II error in hypothesis testing?
- Rejecting a true null hypothesis
- Failing to reject a false null hypothesis (Correct answer)
- Setting too low an alpha level
- Using the wrong statistical test
Correct answer: Failing to reject a false null hypothesis
A Type II error (false negative) occurs when a false null hypothesis is not rejected; its probability equals beta (β).
Question 4: In a linear calibration curve, R² = 0.998 indicates:
- 99.8% of the variation in response is explained by the analyte concentration (Correct answer)
- The assay has 99.8% sensitivity
- The curve has 0.2% error at all concentrations
- The slope is 0.998
Correct answer: 99.8% of the variation in response is explained by the analyte concentration
R² (coefficient of determination) represents the proportion of variance in the dependent variable explained by the independent variable.
Question 5: Which statistical approach is used to adjust for multiple comparisons to control the false discovery rate?
- Bonferroni correction
- Benjamini-Hochberg procedure (Correct answer)
- Tukey HSD test
- Dunnett test
Correct answer: Benjamini-Hochberg procedure
The Benjamini-Hochberg procedure controls the false discovery rate (FDR) and is less conservative than Bonferroni correction.
Question 6: When external quality assurance (EQA) results show a consistent positive bias compared to peer group means, the most likely cause is:
- Random pipetting errors
- A systematic calibration error (Correct answer)
- Imprecise temperature control
- Transcription errors in result reporting
Correct answer: A systematic calibration error
Consistent positive bias relative to peers indicates a systematic error, most commonly due to calibration offset or reagent lot differences.
Question 7: In a scatter plot showing two variables, a Pearson r = −0.85 indicates:
- A weak positive relationship
- A strong negative linear relationship (Correct answer)
- No meaningful relationship
- A perfect inverse relationship
Correct answer: A strong negative linear relationship
Pearson r = −0.85 indicates a strong negative linear relationship, with higher values of X consistently associated with lower values of Y.
STP Data Analysis 5
A study reports a relative risk (RR) of 2.0 with a 95% CI of 1.2–3.5.
What can be concluded?