Noroviruses cause roughly 21 million cases of gastroenteritis (“stomach flu”) an

Question

Noroviruses cause roughly 21 million cases of gastroenteritis (“stomach flu”) annually in the United States. A study examined the effectiveness of a new norovirus vaccine. Healthy adult volunteers received, at random, either the vaccine or a placebo. They were then exposed to the norovirus. In all, 14 of the 38 vaccinated subjects suffered from gastroenteritis compared with 27 of the 39 subjects who received a placebo. Does this study provide evidence that an outcome of gastroenteritis depends on the treatment received? The chi-square test in this situation is

valid because the study is a randomized experiment.

not valid because the sample sizes are small.

valid because the sample is random and the expected counts are large enough.

not valid because some observed counts are too small.

Explanation / Answer

Answer valid because the sample is random and the expected counts are large enough.

Reason Since this is a 2*2 table chi-square test, the expected count should be greater than 10 for the test to be valid.

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