CSR Research Methods & Evidence-Based Practice 2 ā Questions and Answers
Question 1: In a randomized controlled trial evaluating a low-phosphorus diet in CKD patients, the primary outcome is serum phosphorus reduction. What is the most appropriate method to account for dropouts and maintain the integrity of the original randomization?
- Per-protocol analysis
- Intention-to-treat analysis (Correct answer)
- As-treated analysis
- Sensitivity analysis only
Correct answer: Intention-to-treat analysis
Intention-to-treat analysis preserves randomization and prevents bias introduced by selective dropout, making it the gold standard for RCT primary outcomes.
Question 2: A renal dietitian wants to evaluate the strength of a study's causal claim that dietary protein restriction slows GFR decline. Which study design provides the highest level of evidence for causality?
- Cross-sectional survey
- Prospective cohort study
- Systematic review of randomized controlled trials (Correct answer)
- Case-control study
Correct answer: Systematic review of randomized controlled trials
A systematic review of RCTs sits at the top of the evidence hierarchy and provides the strongest basis for causal inferences.
Question 3: When appraising a meta-analysis on potassium intake in dialysis patients, a renal dietitian notices an IĀ² statistic of 85%. How should this be interpreted?
- 85% of the overall effect is due to chance
- There is high heterogeneity among the included studies (Correct answer)
- The pooled estimate is highly precise
- 85% of studies favored the intervention
Correct answer: There is high heterogeneity among the included studies
An IĀ² of 75% or higher indicates substantial to considerable heterogeneity, suggesting the studies are measuring the intervention effect under very different conditions.
Question 4: A dietitian is designing a study comparing intradialytic parenteral nutrition (IDPN) versus oral supplements on albumin levels. Which blinding strategy is most feasible in this setting?
- Double-blind (both participants and outcome assessors)
- Triple-blind (including statistician)
- Single-blind (only outcome assessor blinded) (Correct answer)
- Open-label with no blinding
Correct answer: Single-blind (only outcome assessor blinded)
Because patients can identify their nutritional delivery route, blinding only the outcome assessor (single-blind) is the most feasible rigorous option.
Question 5: In a renal nutrition study, researchers report a statistically significant result (p=0.03) but a mean serum phosphorus reduction of only 0.2 mg/dL. What concept best explains why this finding may not be clinically meaningful?
- Type I error inflation
- Lack of statistical power
- Difference between statistical and clinical significance (Correct answer)
- Regression to the mean
Correct answer: Difference between statistical and clinical significance
Statistical significance indicates a result unlikely due to chance, but clinical significance requires the effect size to be large enough to matter in patient care.
Question 6: A cross-sectional study finds that hemodialysis patients with higher dietary sodium intake have higher blood pressure. Which limitation is most critical when interpreting this finding?
- Selection bias due to random sampling
- Cannot establish temporal relationship between sodium and blood pressure (Correct answer)
- Recall bias is eliminated by this design
- The study overestimates prevalence
Correct answer: Cannot establish temporal relationship between sodium and blood pressure
Cross-sectional studies measure exposure and outcome simultaneously, making it impossible to determine which came first or establish causality.
Question 7: A renal dietitian is using the GRADE framework to assess evidence quality for a guideline recommendation on dietary potassium restriction in CKD stage 4. Which factor would DOWNGRADE the quality of evidence?
- Large effect size across studies
- High consistency between study results
- Serious risk of bias in included studies (Correct answer)
- Dose-response relationship observed
Correct answer: Serious risk of bias in included studies
In GRADE, serious risk of bias in the included studies is a primary reason to downgrade the overall certainty of evidence.
CSR Research Methods & Evidence-Based Practice 2
In a randomized controlled trial evaluating a low-phosphorus diet in CKD patients, the primary outcome is serum phosphorus reduction.
What is the most appropriate method to account for dropouts and maintain the integrity of the original randomization?