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hw3key - BIOST/EPI 513 Spring Quarter 2011 Dr McKnight...

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1 BIOST/EPI 513 Spring Quarter 2011 Dr. McKnight HOMEWORK 3 KEY See Appendix I for STATA commands and Appendix II for output. 1. In a matched case-control study of risk factors for benign breast disease (BBD), investigators were interested in whether a woman had given birth affected her risk of the disease. Cases were women diagnosed with fibrocystic benign breast disease; for each case, an age-matched control was identified from women admitted for general surgery, orthopedic or otolaryngologic services to the same hospital as the case. The numbers of cases and matched controls who had and had not ever given birth are given in the table below. (a) The first part of this question asks you to analyze these data adjusting for the matching. i. An estimate of the OR for the association between having had ≥ 1 birth and BBD. 1.8 ii. A 95% Confidence Interval for this OR. (0.74, 4.6) iii. A P-value for the two-sided test of H 0 : OR = 1. 0.230 iv. We observed little evidence that prior birth was associated with benign breast disease in our age-matched case-control data (OR=1.8, 95% CI: 0.74-4.6; p =0.230). (b) Repeat all four parts of (a) above, using an analysis that ignores the fact that controls were matched to cases, and does not adjust for matching variables. ≥1 Birth No Births Total Cases 25 25 50 Controls 18 32 50 Total 43 57 100 i. An estimate of the OR for the association between having had ≥ 1 birth and BBD. 1.8 ii. A 95% Confidence Interval for this OR. (0.74, 4.3) iii. A P-value for the two-sided test of H 0 : OR = 1. 0.157 iv. Without accounting for age, women who had given birth were 1.8 times as likely to develop benign breast disease than women who never gave birth (95% CI: 0.74-4.3; p =0.157). (c) Odds ratio estimates from (a) and (b) are equal, but the CI in (a) is slightly wider. Note that accounting for the matching in case-control studies can decrease or increase the standard error of the estimated log OR; here it slightly increases it.
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2 2. In the same study that produced the ejection fraction assessments discussed in lecture, coronary arteriography was used to determine how many of the three major arterial systems of the heart were significantly narrowed. The table below gives the numbers of subjects
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