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Homework 8 Solutions

# Homework 8 Solutions - HW 8 SOLUTIONS Chi-Square r x c...

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HW 8 SOLUTIONS Chi-Square: r x c Tables and Goodness of Fit 1. 10.47. Herpes simplex virus type 2 (HSV-2) is a sexually transmitted disease. As part of the third National Health and Nutrition Examination Survey (NHANES III), prevalence of HSV-2 was determined in four regions of the United States. The data are given in the following table Note, this is a slightly rearranged version of the table given in the text. HSV-2 No HSV-2 Northeast 323 1165 Midwest 381 1689 South 1320 4003 West 712 1986 a. Use a chi-square test to compare the prevalence rates at α = 0.01. Correct: (1) α = 0.01 (2) H 0 : HSV-2 prevalence is the same in the four regions H A : HSV-2 prevalence differs across the four regions (3) X 2 s = 49.77 (4) P = 8.95E-11 = 0.0000000000895 which we interpret as P < 0.001 (5) P < α , reject H 0 (6) There is significant evidence to conclude that HSV-2 prevalence differs across the four regions 2. 10.51. A randomized, double-blind, placebo-controlled experiment was conducted in which patients with Alzheimer's disease were given either extract of Ginkgo biloba (EGb) or a placebo for one year. The change in each patient's Alzheimer's Disease Assessment Scale–Cognitive subscale (ADAS-Cog) score was measured. The results are given in the table. Note : If the ADAS-Cog went down, then the patient improved. Change in ADAS-Cog Score -4 or better -2 to -3 -1 to 1 2 to 3 3 to 4 EGb 22 18 12 7 16 Placebo 10 11 19 11 24 a. Use a chi-square test to compare the prevalence rates at α = 0.05 Correct: (1) α = 0.05 (2) H 0 : Distribution of change in ADAS-Cog score is same for EGb or placebo H A : Distribution of change in ADAS-Cog score is different for EGb or placebo (3) X 2 s = 10.26 (4) P = 0.0363 (DoStat calculator) (5) P < α , so reject H 0 (6) There is significant evidence to conclude that EGb and placebo are not equally effective.

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