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Discussion Starter #1
In a study of the effect of physical activity on the incidence of osteoporosis, investigators follow a large group of postmenopausal women and find that those with an active lifestyle have lower risk of osteoporosis. What other finding would fulfill an important criterion for establishing that the association between active lifestyle and lower osteoporosis risk is causal?

A. Any amount of regular physical exercise protects people from osteoporosis
B. Assuming the influence of a previously unknown biological mechanism
C. Similar associations between active lifestyle and decreased risk of osteoporosis
D. The relative risk of osteoporosis for people with an active lifestyle is 1.3
E. Women with active lifestyles are more likely to eat a bone-healthy diet than women with sedentary lifestyles
 

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C. Similar associations between active lifestyle and decreased risk of osteoporosis
 

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Discussion Starter #4
well its C...

Option C (Similar associations between active lifestyle and decreased risk of osteoporosis) is correct.Criteria that suggest a statistical association is causal include strength, consistency, correct temporal sequence, and biological plausibility. Similar associations found in different studies with different designs fulfill the criteria of consistency of results.

Option A (Any amount of regular physical exercise protects people from osteoporosis) is incorrect.Although true, this statement does not address directly any of the criteria for causation.

Option B (Assuming the influence of a previously unknown biological mechanism) is incorrect. The inability to explain the association through the operation of known biological mechanisms violates the criterion of biological plausibility.

Option D (The relative risk of osteoporosis for people with an active lifestyle is 1.3) is incorrect. This statement suggests that the association between active lifestyle and osteoporosis is not strong. Strength of association is one of the criteria for causation.

Option E (Women with active lifestyles are more likely to eat a bone-healthy diet than women with sedentary lifestyles) is incorrect. This option suggests that the association between active lifestyle and lower osteoporosis risk is confounded by dietary differences between the groups. This would reduce the likelihood that the association is causal.
 
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