an experiment investigates a dietary approach to treating anxiety disorder. researchers randomly assigned 25 subjects to two treatment groups, one taking a high dose of vitamin c and the other a placebo. suppose some of the 25 subjects were very active people who walked a lot or got vigorous exercise several times a week, while others tended to be more sedentary, working office jobs and watching a lot of tv. why might researchers choose to block the subjects by activity level before randomly assigning them to the vitamin c and placebo groups?

why might researchers choose to block the subjects by activity level before randomly assigning them to the vitamin c and placebo groups?

a. there is no reason why researchers might choose to block this experiment.

b. its important to keep anyone who could affect the outcome or the measurement of the response from knowing which subjects have been assigned to which treatments.

c. people who have anxiety disorder might differ from others with respect to activity level, and that additional variability could increase the effectiveness of this treatment.

d. people who engage in regular exercise might differ from others with respect to anxiety disorder, and that additional variability could obscure the effectiveness of this treatment.

Question

an experiment investigates a dietary approach to treating anxiety disorder. researchers randomly assigned 25 subjects to two treatment groups, one taking a high dose of vitamin c and the other a placebo. suppose some of the 25 subjects were very active people who walked a lot or got vigorous exercise several times a week, while others tended to be more sedentary, working office jobs and watching a lot of tv. why might researchers choose to block the subjects by activity level before randomly assigning them to the vitamin c and placebo groups?

why might researchers choose to block the subjects by activity level before randomly assigning them to the vitamin c and placebo groups?

a. there is no reason why researchers might choose to block this experiment.

b. its important to keep anyone who could affect the outcome or the measurement of the response from knowing which subjects have been assigned to which treatments.

c. people who have anxiety disorder might differ from others with respect to activity level, and that additional variability could increase the effectiveness of this treatment.

d. people who engage in regular exercise might differ from others with respect to anxiety disorder, and that additional variability could obscure the effectiveness of this treatment.

Accepted Answer

# Brief Explanations:
To solve this, we analyze each option:
- Option A is incorrect as blocking (stratifying by a variable) has a purpose in experiments.
- Option B describes blinding, not blocking, so it's incorrect.
- Option C's reasoning about increasing treatment effectiveness due to variability is wrong; variability usually obscures effects.
- Option D: Blocking by activity level (exercise) is done because regular exercisers might differ in anxiety levels, and this variability could hide the treatment's true effect. Blocking controls for this confounding variable.

# Answer:
D. People who engage in regular exercise might differ from others with respect to anxiety disorder, and that additional variability could obscure the effectiveness of this treatment.

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