Statistics Research & Evidence-Based Practice 2 — Questions and Answers
Question 1: A researcher reports a 95% confidence interval of [2.1, 5.8] for a treatment effect. What does this mean?
- There is a 95% chance the true parameter lies in this interval
- If the study were repeated many times, 95% of such intervals would contain the true parameter (Correct answer)
- The sample mean falls within this interval 95% of the time
- The treatment works in 95% of patients
Correct answer: If the study were repeated many times, 95% of such intervals would contain the true parameter
A 95% CI means that 95% of intervals constructed from repeated samples would contain the true population parameter.
Question 2: Which study design provides the strongest evidence for establishing causation?
- Cross-sectional survey
- Case-control study
- Randomized controlled trial (Correct answer)
- Prospective cohort study
Correct answer: Randomized controlled trial
Randomized controlled trials minimize confounding through random assignment, providing the strongest causal evidence.
Question 3: What is the primary purpose of blinding participants in a clinical trial?
- To reduce sample size requirements
- To prevent selection bias
- To reduce placebo and reporting bias (Correct answer)
- To improve external validity
Correct answer: To reduce placebo and reporting bias
Blinding prevents participants (and sometimes assessors) from knowing treatment assignments, reducing placebo and reporting biases.
Question 4: In meta-analysis, what does a forest plot primarily display?
- The distribution of raw data across studies
- Effect sizes and confidence intervals from individual studies alongside a pooled estimate (Correct answer)
- The correlation between study quality and effect size
- Publication bias detection results
Correct answer: Effect sizes and confidence intervals from individual studies alongside a pooled estimate
A forest plot displays individual study effect sizes with their CIs and a pooled overall estimate, enabling visual comparison.
Question 5: A systematic review differs from a narrative review primarily because it:
- Includes only randomized controlled trials
- Uses pre-specified, reproducible methods to identify and synthesize evidence (Correct answer)
- Requires a larger number of included studies
- Is always conducted by multiple authors
Correct answer: Uses pre-specified, reproducible methods to identify and synthesize evidence
Systematic reviews use transparent, reproducible search and selection criteria that reduce bias in evidence synthesis.
Question 6: What does the I² statistic measure in a meta-analysis?
- The average effect size across studies
- The proportion of variability in effect estimates due to heterogeneity rather than chance (Correct answer)
- The number of studies needed to overturn a finding
- Publication bias in the study pool
Correct answer: The proportion of variability in effect estimates due to heterogeneity rather than chance
I² quantifies the percentage of total variation across studies attributable to heterogeneity rather than sampling error.
Question 7: A researcher uses convenience sampling by surveying students in one university class. Which threat to validity is MOST relevant?
- Internal validity — confounding
- Statistical conclusion validity — low power
- External validity — limited generalizability (Correct answer)
- Construct validity — measurement error
Correct answer: External validity — limited generalizability
Convenience samples from a narrow population limit how broadly findings can be generalized, threatening external validity.
Statistics Research & Evidence-Based Practice 2
A researcher reports a 95% confidence interval of [2.1, 5.8] for a treatment effect.
What does this mean?