ISSA Research Methods & Evidence-Based Practice 2 — Questions and Answers
Question 1: In a crossover study design, what is the primary purpose of a washout period?
- To increase statistical power
- To eliminate carryover effects from the previous treatment (Correct answer)
- To randomly assign participants to groups
- To blind researchers to group assignment
Correct answer: To eliminate carryover effects from the previous treatment
A washout period allows residual effects of the prior treatment to clear before participants begin the next condition.
Question 2: Which statistical measure describes the proportion of variance in an outcome explained by a predictor variable?
- Cohen's d
- Pearson r
- R-squared (R²) (Correct answer)
- Standard error of the mean
Correct answer: R-squared (R²)
R² (coefficient of determination) quantifies how much of the dependent variable's variance is accounted for by the independent variable(s).
Question 3: A nutrition study reports a 95% confidence interval of 1.2–3.8 kg for weight loss. What does this mean?
- 95% of participants lost between 1.2 and 3.8 kg
- There is a 95% probability the true mean effect falls between 1.2 and 3.8 kg (Correct answer)
- The study's p-value is less than 0.05
- The result is not clinically significant
Correct answer: There is a 95% probability the true mean effect falls between 1.2 and 3.8 kg
A 95% CI means that if the study were repeated many times, 95% of such intervals would contain the true population parameter.
Question 4: Which type of bias occurs when participants in a study behave differently because they know they are being observed?
- Recall bias
- Selection bias
- Hawthorne effect (Correct answer)
- Attrition bias
Correct answer: Hawthorne effect
The Hawthorne effect describes behavior change resulting from the awareness of being observed in a study.
Question 5: In evidence-based practice, a 'number needed to treat' (NNT) of 10 means:
- 10% of patients respond to the treatment
- Ten patients must receive treatment to prevent one additional adverse outcome (Correct answer)
- The treatment is effective in 10 clinical trials
- The intervention takes 10 weeks to produce results
Correct answer: Ten patients must receive treatment to prevent one additional adverse outcome
NNT indicates how many patients need to be treated to achieve one beneficial outcome that would not have occurred otherwise.
Question 6: Which study design is MOST appropriate for investigating rare adverse outcomes of a nutritional supplement?
- Randomized controlled trial
- Cross-sectional survey
- Case-control study (Correct answer)
- Ecological study
Correct answer: Case-control study
Case-control studies are efficient for rare outcomes because they start with cases who already have the outcome and compare them to controls.
Question 7: What is the main limitation of self-reported dietary intake data collected via food frequency questionnaires (FFQs)?
- They cannot capture macro-nutrient information
- They are too expensive for large studies
- They rely on participant memory and may underestimate intake (Correct answer)
- They require laboratory analysis of food samples
Correct answer: They rely on participant memory and may underestimate intake
FFQs depend on participants accurately recalling habitual dietary patterns, which introduces recall bias and systematic underreporting.
ISSA Research Methods & Evidence-Based Practice 2
In a crossover study design, what is the primary purpose of a washout period?