ACBN Research & Evidence-Based Practice 3 ā Questions and Answers
Question 1: A nutritionist calculates the number needed to treat (NNT) for a dietary fiber intervention to prevent one case of type 2 diabetes. An NNT of 20 means:
- 20% of participants benefited from the intervention
- 20 people must be treated to prevent one additional case (Correct answer)
- The intervention reduces risk by 20 percentage points
- The control group had 20 more cases than the treatment group
Correct answer: 20 people must be treated to prevent one additional case
NNT indicates how many patients must receive the intervention for one patient to benefit, compared to the control condition.
Question 2: Which dietary assessment method has the highest risk of recall bias?
- Weighed food record kept prospectively
- 24-hour dietary recall
- Doubly labeled water method
- Food frequency questionnaire for the past year (Correct answer)
Correct answer: Food frequency questionnaire for the past year
Food frequency questionnaires asking about the past year require participants to recall habitual diet over a long period, maximizing recall bias.
Question 3: In nutrition research, the 'doubly labeled water' method is considered a gold standard for measuring:
- Dietary protein intake
- Total energy expenditure (Correct answer)
- Body fat percentage
- Micronutrient bioavailability
Correct answer: Total energy expenditure
Doubly labeled water measures CO2 production via isotope elimination rates, providing an objective measure of total energy expenditure.
Question 4: Regression to the mean in nutrition intervention studies refers to:
- Participants returning to baseline diet after study completion
- Extreme values at baseline tending to move closer to average on re-measurement (Correct answer)
- Statistical adjustment for confounding variables
- Averaging results across multiple study sites
Correct answer: Extreme values at baseline tending to move closer to average on re-measurement
Regression to the mean occurs when participants with extreme initial values naturally trend toward the population average on subsequent measurement, independent of any intervention.
Question 5: A cohort study follows 5,000 adults for 10 years and finds that those eating >3 servings of whole grains daily had a relative risk of 0.65 for cardiovascular disease. This means:
- Whole grain eaters had 65% more cardiovascular disease
- Whole grain eaters had 35% lower risk of cardiovascular disease compared to non-consumers (Correct answer)
- 65% of whole grain eaters did not develop cardiovascular disease
- The intervention reduced absolute risk by 0.65%
Correct answer: Whole grain eaters had 35% lower risk of cardiovascular disease compared to non-consumers
A relative risk of 0.65 means the exposed group has 65% of the risk of the unexposed group, representing a 35% relative risk reduction.
Question 6: Which principle of research ethics requires that participants receive complete and accurate information before agreeing to participate?
- Beneficence
- Justice
- Informed consent (Correct answer)
- Autonomy
Correct answer: Informed consent
Informed consent requires that participants receive full disclosure of study risks, benefits, and procedures before voluntarily agreeing to participate.
Question 7: A systematic review finds significant heterogeneity (IĀ² = 82%) across included studies on calcium supplementation and bone density. This indicates:
- 82% of studies showed statistically significant results
- High variability in results across studies that may limit pooling of data (Correct answer)
- The meta-analysis has an 82% confidence level
- 18% of studies are outliers to be excluded
Correct answer: High variability in results across studies that may limit pooling of data
IĀ² values above 75% indicate high heterogeneity, meaning substantial variability in results across studies that should prompt investigation of potential moderators.
ACBN Research & Evidence-Based Practice 3
A nutritionist calculates the number needed to treat (NNT) for a dietary fiber intervention to prevent one case of type 2 diabetes.
An NNT of 20 means: