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Old 10-19-2012
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Arrow Gyrus Daily Questions; Epidemiology #2

Two separate randomized double-blind trials were done to see if administration of vitamin C after a myocardial infarction (MI) decreased risk for another MI. Both trials showed that vitamin C reduced the risk by 5%. This reduction was significant in one trial (P < 0.05); in the other, it was not significant. The best explanation for this difference between the results of the two trials is that

(A) the researchers were "blind" in one trial but not in the other
(B) randomization did not evenly distribute the risk factors between the two trials
(C) the sample sizes in the two trials were different
(D) there was a placebo effect in one trial but not in the other
(E) the concentration of vitamin C was dif-ferent between the two trials
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(C) the sample sizes in the two trials were different
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Old 10-20-2012
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yep....its C
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C seems to be the most likely answer
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different sample sizes...

as you increase sample size, you can show statistical difference between anything... even between 0.00000099 and 0.00000098
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The answer is C.
The sample sizes in two trials were different.

The best explanation for this difference between the studies is that the sample sizes in the two studies were different. The larger the sample size, the higher the power, and the less likely a type I error. This decreased likelihood is reflected in a lower P value, and thus, a higher likelihood of significance for studies with a large sample size. Problems with randomization, efficacy, blinding, or placebo effects would have differen-tially affected the risk. However, the risk was equal (5%) in the two studies.
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(C) the sample sizes in the two trials were different
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