Question 1

Which of the following best describes a confounding variable in the context of a study examining the effect of a low-fat diet on breast cancer recurrence?

Accepted Answer

A variable that is not present in the analysis but may influence the relationship between the diet and cancer recurrence.

Question 2

In the case-control study on childhood ALL (acute lymphoblastic leukemia), why can't relative risk be directly calculated from the data?

Accepted Answer

Because participants were selected based on disease status, not exposure.

Question 3

A researcher is planning an experiment to test the effect of a new fertilizer on plant growth. To minimize the impact of soil type as a confounding variable, which strategy should she use?

Accepted Answer

Randomize fertilizer assignment within groups of similar soil type (blocking).

Question 4

In the Women's Intervention Nutrition Study, which of the following is a covariate that was collected and analyzed?

Accepted Answer

Type of initial cancer (hormonal receptor status).

Question 5

Which of the following best describes the design of the agronomist's wheat experiment with three pest management strategies and three wheat varieties?

Accepted Answer

A field experiment using randomization, replication, and blocking.

Question 6

Suppose a study finds a strong association between dietary fat intake and breast cancer recurrence. Which of the following statements is true regarding causation?

Accepted Answer

Strong association is necessary but not sufficient to establish causation.

Question 7

In a randomized controlled trial, what is the primary purpose of randomization?

Accepted Answer

To equalize the effects of unknown confounding variables across treatment groups.

Question 8

A study measures the effect of caffeine on heart rate by having each subject drink both regular and decaf coffee in random order. What type of design is this?

Accepted Answer

A paired (within-subject) design.

Question 9

Which of the following is an example of pseudo-replication in an experiment?

Accepted Answer

Measuring the same experimental unit multiple times and treating each measurement as independent.

Question 10

In the context of confounding, which equation best represents the odds ratio (OR) for a case-control study?

Accepted Answer

$$OR = \frac{(a/b)}{(c/d)}$$ where $$a$$ and $$b$$ are cases with and without exposure, $$c$$ and $$d$$ are controls with and without exposure.

Question 11

A study finds that weight loss is more common in the intervention group than the control group. Why might this be a source of confounding?

Accepted Answer

Because weight loss may independently affect the outcome, making it difficult to separate the effect of the intervention from the effect of weight loss.

Question 12

Which of the following strategies is LEAST effective for controlling confounding variables in an experiment?

Accepted Answer

Ignoring potential confounders.

Question 13

In a case-control study, which group is selected based on the outcome?

Accepted Answer

Both cases and controls.

Question 14

Which of the following is a key difference between a cohort study and a case-control study?

Accepted Answer

Cohort studies select participants based on exposure, while case-control studies select based on outcome.

Question 15

A researcher wants to generalize the results of a cross-sectional survey to the entire population. What must she consider to ensure valid generalization?

Accepted Answer

Sampling bias and non-response bias.

Question 16

Which of the following statements about blinding in field experiments is correct?

Accepted Answer

Blinding may be feasible for outcome assessors but not for those administering treatments.

Question 17

In the context of experimental design, what is the main advantage of blocking?

Accepted Answer

It accounts for variation in experimental conditions by grouping similar units together before randomization.

Question 18

Which of the following is a real-world example of a lurking variable in a study examining the relationship between exercise and heart health?

Accepted Answer

Dietary habits that are not measured but may influence heart health.

Question 19

A study finds that breast-conserving surgery is associated with a greater risk of locoregional recurrence than mastectomy. Why is it important to adjust for surgical procedure in the analysis of dietary intervention effects?

Accepted Answer

Because surgical procedure may confound the relationship between diet and recurrence, leading to biased estimates if not adjusted for.

Confounding Variables, Study Design, and Strength of Evidence in Statistics

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