ACBN Research & Evidence-Based Practice 2 — Questions and Answers
Question 1: A nutritionist wants to determine if a new dietary intervention reduces LDL cholesterol. Which study design provides the strongest causal evidence?
- Cross-sectional survey
- Randomized controlled trial (Correct answer)
- Case-control study
- Ecological study
Correct answer: Randomized controlled trial
Randomized controlled trials (RCTs) provide the strongest causal evidence because random assignment minimizes confounding variables.
Question 2: In a clinical nutrition study, 'blinding' refers to:
- Excluding outlier data points from analysis
- Preventing participants or researchers from knowing group assignments (Correct answer)
- Removing confounding variables statistically
- Concealing the study hypothesis from participants
Correct answer: Preventing participants or researchers from knowing group assignments
Blinding prevents knowledge of group assignment, reducing bias in outcome assessment and participant behavior.
Question 3: A meta-analysis of omega-3 supplementation trials reports a pooled effect size with a 95% confidence interval of 0.1 to 0.9 mmol/L triglyceride reduction. This means:
- There is a 95% probability the true effect is zero
- We are 95% confident the true population effect falls within that range (Correct answer)
- 5% of individual studies showed no effect
- The result is statistically significant only 95% of the time
Correct answer: We are 95% confident the true population effect falls within that range
A 95% confidence interval means we are 95% confident the true population parameter lies within the stated range.
Question 4: Which type of bias occurs when participants who drop out of a nutrition study differ systematically from those who complete it?
- Recall bias
- Attrition bias (Correct answer)
- Selection bias
- Observer bias
Correct answer: Attrition bias
Attrition bias occurs when dropouts differ from completers, potentially skewing results toward those who tolerated the intervention.
Question 5: The PRISMA statement is a reporting guideline used for:
- Randomized controlled trials in clinical nutrition
- Systematic reviews and meta-analyses (Correct answer)
- Observational cohort studies
- Dietary assessment validation studies
Correct answer: Systematic reviews and meta-analyses
PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) provides a checklist and flow diagram for transparent reporting of systematic reviews.
Question 6: A nutritionist reviewing a study finds a p-value of 0.03 for a dietary intervention effect. The correct interpretation is:
- There is a 3% chance the null hypothesis is true
- There is a 97% probability the intervention works
- The probability of observing results this extreme, if the null hypothesis were true, is 3% (Correct answer)
- The effect size is clinically meaningful
Correct answer: The probability of observing results this extreme, if the null hypothesis were true, is 3%
A p-value represents the probability of obtaining results at least as extreme as observed, assuming the null hypothesis is true.
Question 7: Which hierarchy of evidence level is correctly ranked HIGHEST to LOWEST?
- Expert opinion → cohort study → RCT → systematic review
- Systematic review → RCT → cohort study → expert opinion (Correct answer)
- RCT → systematic review → case report → expert opinion
- Cohort study → RCT → meta-analysis → expert opinion
Correct answer: Systematic review → RCT → cohort study → expert opinion
Systematic reviews and meta-analyses of RCTs rank highest, followed by RCTs, cohort studies, and expert opinion at the lowest level.
ACBN Research & Evidence-Based Practice 2
A nutritionist wants to determine if a new dietary intervention reduces LDL cholesterol.
Which study design provides the strongest causal evidence?