ACBN Research & Evidence-Based Practice 5 — Questions and Answers
Question 1: A cross-over study design is particularly advantageous in nutrition research because it:
- Eliminates the need for a control group entirely
- Allows each participant to serve as their own control, reducing between-subject variability (Correct answer)
- Is the only design suitable for studying rare disease outcomes
- Removes the need for statistical analysis of results
Correct answer: Allows each participant to serve as their own control, reducing between-subject variability
Crossover designs have each participant experience all interventions sequentially, reducing variability from individual differences and increasing statistical power.
Question 2: Sensitivity analysis in a meta-analysis of dietary studies is used to:
- Test whether individual study results are clinically sensitive to patient characteristics
- Assess how robust the overall findings are when specific studies or assumptions are changed (Correct answer)
- Measure the sensitivity of dietary assessment instruments
- Determine the minimum detectable effect size across studies
Correct answer: Assess how robust the overall findings are when specific studies or assumptions are changed
Sensitivity analysis tests whether the meta-analytic conclusions change when specific studies, inclusion criteria, or statistical assumptions are varied.
Question 3: Which of the following is an example of an ecological fallacy in nutritional epidemiology?
- Concluding that increased vegetable intake causes cancer prevention based on a cell culture study
- Concluding that individuals in a country eat less fat because national fat supply data correlates inversely with national heart disease rates (Correct answer)
- Concluding that a supplement works because it had statistical significance in one trial
- Concluding that randomized evidence does not apply to the real-world population
Correct answer: Concluding that individuals in a country eat less fat because national fat supply data correlates inversely with national heart disease rates
Ecological fallacy occurs when group-level associations are incorrectly applied to individuals, as population-level data cannot prove individual-level relationships.
Question 4: In nutrition research, 'internal validity' refers to:
- Whether the study results can be generalized to other populations
- The degree to which a study accurately measures what it intends to measure within its own sample (Correct answer)
- The validity of the dietary assessment tool used
- Whether the statistical analysis was performed correctly
Correct answer: The degree to which a study accurately measures what it intends to measure within its own sample
Internal validity refers to the confidence that observed associations within the study are causal and not due to bias or confounding.
Question 5: A nutritionist reviewing an industry-funded study on a supplement finds consistently favorable results compared to independent studies. This is most likely an example of:
- Allegiance bias or funding bias affecting study design and reporting (Correct answer)
- Confirmation that the supplement is effective based on superior research methods
- Reporting bias introduced by journal peer reviewers
- Sampling bias due to industry access to higher-risk patients
Correct answer: Allegiance bias or funding bias affecting study design and reporting
Funding bias (allegiance bias) occurs when studies funded by entities with a financial interest show systematically more favorable results than independently funded studies.
Question 6: The Hawthorne effect in a dietary intervention study refers to:
- Participants changing their eating behavior simply because they know they are being observed (Correct answer)
- Contamination of the control group by the treatment intervention
- Seasonal variation in dietary habits affecting study results
- Loss of statistical power due to participant dropout
Correct answer: Participants changing their eating behavior simply because they know they are being observed
The Hawthorne effect describes behavioral changes that occur because participants are aware they are being studied, independent of the intervention itself.
Question 7: Which of the following represents the appropriate use of a food frequency questionnaire (FFQ) in nutrition research?
- Measuring precise daily nutrient intake in a metabolic ward study
- Ranking individuals by usual dietary patterns in large epidemiological studies (Correct answer)
- Assessing short-term dietary changes in clinical intervention trials
- Validating total energy expenditure against biomarkers
Correct answer: Ranking individuals by usual dietary patterns in large epidemiological studies
FFQs are best suited to rank individuals by habitual dietary intake in large epidemiological studies, where precision of individual day intake is less critical than relative dietary patterns.
ACBN Research & Evidence-Based Practice 5
A cross-over study design is particularly advantageous in nutrition research because it: