exam2.reviewproblems.solutions

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

This preview shows pages 1–3. Sign up to view the full content.

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

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
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
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 7

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

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online