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Unformatted text preview: is, the distribution for the response is the same for all 3 populations, what is the expected value of the test statistic? The test statistic is X2. If H0 is true the test statistic will have a chi‐squared distribution with (3‐1)(4‐1)=6 degrees of freedom. So if H0 is true, we would expect the test statistic to be about 6. 214 Try It! Treatment for Shingles An article had the headline “For adults, chicken pox vaccine may stop shingles”. A clinical trial was conducted in which 420 subjects were randomly assigned to receive the chicken pox vaccine or a placebo vaccine. Some side effects of interest were swelling and rash around the injection site. Consider the following results for the swelling side effect. Treatment Group * Swelling Status Crosstabulation
Count Treatment
Group vaccine
placebo Total Swelling Status
minor
swelling
no swelling
42
134
32
142
74
276 major
swelling
54
16
70 Total
230
190
420 ChiSquare Tests Pearson ChiSquare
Likelihood Ratio
LinearbyLinear
Association
N of Valid Cases Value
18.571
19.556
17.696 2
2 Asymp. Sig.
(2sided)
.00009
.00006 1 .00003 df 420 a. Give the name of the test to be used for assessing if the distribution of swelling status is the same for the two treatment populations. Chi‐squared test of homogeneity b. Based on the above data, among those chicken pox vaccinated subjects, what percent had major swelling around the injection site? 54/230 = 0.2348 c. Based on the above data, among those placebo vaccinated subjects, what percent had major swelling around the injection site? 16/190 = 0.0842 d. Assuming the distribution of swelling status is the same for the two treatment populations, how many chicken pox vaccinated subjects would you expect to have major swelling around the injection site? Show your work. (230 x 70)/420 = 38.33 e. Use a level of 0.05 to assess if the distribution of swelling status is the same for the two treatment populations. Test Statistic Value: __18.571 _ p‐value: __0.00009__ Thus, the distribution of swelling status (circle your answer): does does not app...
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This document was uploaded on 02/25/2014 for the course STATS 250 at University of Michigan.
 Summer '10
 Gunderson
 Statistics

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