exam2.reviewproblems.solutions

exam2.reviewproblems.solutions - PubH 6450 Fall 2008 Test 2...

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PubH 6450 – Fall 2008 – Test 2 Review Problems - Answer Key A. 1. Two random samples of parents/kids (participated in program, did not participate) 2. Binary outcome: fully vaccinated, yes or no 3. Large samples, all of the following 5: n 1 ˆ p 1 = X 1 = 73 n 1 (1 - ˆ p 1 ) = n 1 - X 1 = 20 n 2 ˆ p 2 = X 2 = 30 n 2 (1 - ˆ p 2 ) = n 2 - X 2 = 41 4. Two-sample normal approximation to binomial, H 0 : p 1 = p 2 vs. H a : p 1 > p 2 ˆ p 1 = 73 / 93 = 0 . 785 ˆ p 2 = 30 / 71 = 0 . 423 ˆ p = (73 + 30) / (93 + 71) = 0 . 628 z = 0 . 785 - 0 . 423 p (0 . 628)(0 . 372)(1 / 93 + 1 / 71) = 4 . 76 p - value = Pr( Z > 4 . 76) 0 We have substantial evidence showing greater vaccination rates for children of parents who participated in the education program compared to children of parents who did not participate in the education program. 1
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1. Sampled and matched on disease status and then exposure determined: Case Control Study 2. Binary outcome: exposure to county fair, yes or no 3. Large samples, all counts a, b, c and d 10 4. 95% Confidence Interval for the Odds Ratio Odds Exposed | Rash = 25 / 50 = 0 . 50 Odds Exposed | Norash = 16 / 59 = 0 . 27 ˆ OR = 0 . 50 / 0 . 27 = 1 . 85 Ln ( ˆ OR ) = ln (1 . 85) = 0 . 6152 Ln ( ˆ OR ) ± Z * p 1 /a + 1 /b + 1 /c + 1 /d 0 . 6152 ± 1 . 96 p 1 / 25 + 1 / 16 + 1 / 50 + 1 / 59 0 . 6152 ± 1 . 96(0 . 3734) = ( - 0 . 1167 , 1 . 3471) The confidence interval above is on the log scale. Back transform to the original scale by taking the exponential of the lower and upper bound. [ exp ( - 0 . 1167) , exp (1 . 3471)] = (0 . 89 , 3 . 85) The estimate and 95% confidence interval for the odds ratio are 1.85 (0.89, 3.85). This confidence interval contains the null value of 1. There is not sufficient evidence to conclude exposure to the county fair is associated with the rash. 2
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This note was uploaded on 11/21/2011 for the course PUBH 6450 taught by Professor Andymugglin during the Fall '10 term at Minnesota.

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exam2.reviewproblems.solutions - PubH 6450 Fall 2008 Test 2...

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