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part17(1) - Public Health 6450 Fall 2011 Lynn Eberly and...

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Public Health 6450 Fall 2011 Lynn Eberly and Andy Mugglin Division of Biostatistics School of Public Health University of Minnesota [email protected] Part 17
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Review Paired Samples in Two-by-Two Tables Where are we going? Previously: Chi-square tests for H 0 : independence in two-by-two tables (Ch. 9.1-9.2) Chi-square tests for H 0 : p 1 = p 2 in two-by-two tables (Ch. 9.2) Chi-square tests for larger tables (Ch. 9.1-9.2) Current topics: Chi-square tests for paired sample two-by-two tables (not in M,M&C) Binomial exact test for paired sample two-by-two tables (not in M,M&C) Next topics (after Exam II): Overview of Analysis Methods (so far) Describing Relationships Between Quantitative Variables Eberly and Mugglin PubH 6450 Fall 2011 Part 17 2 / 22
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Review Paired Samples in Two-by-Two Tables Motivating the chi-square test McNemar’s test for paired two-by-two tables Detailed Example The Binomial exact test for paired two by two tables Paired Samples and Binomial Outcomes Recall that paired samples have two measures taken on one ‘unit.’ For continuous measures, such studies may collect, for example: a before and after measure of a test score with a new teaching intervention (unit = student) a depression scale taken on each of two twins (unit = twin pair) pack-years of cigarette smoking for each of a lung cancer case and a matched control (unit = case with matched control). In this section, we are concerned with two measures that are binary and are taken on the same unit. Eberly and Mugglin PubH 6450 Fall 2011 Part 17 3 / 22
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Review Paired Samples in Two-by-Two Tables Motivating the chi-square test McNemar’s test for paired two-by-two tables Detailed Example The Binomial exact test for paired two by two tables Nonfat versus Whole Fat Yogurt Participants in a nutrition survey each answered two questions: “Does whole fat yogurt taste good or bad to you?” “Does non-fat yogurt taste good or bad to you?” Nonfat Whole Fat Good Bad Total Good 55 12 67 Bad 5 28 33 Total 60 40 100 This is a matched pairs study: each participant was asked both questions, and thus was matched to him- or herself. How many participants? How many pairs? Eberly and Mugglin PubH 6450 Fall 2011 Part 17 4 / 22
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Review Paired Samples in Two-by-Two Tables Motivating the chi-square test McNemar’s test for paired two-by-two tables Detailed Example The Binomial exact test for paired two by two tables Subsequent Surgery after Initial Sinus Surgery Patients undergoing bilateral sinus surgery for chronic rhinosinusitis may have one side (e.g., left) treated with Treatment A and the other (e.g., right) with Treatment B to see if A is better than B at preventing subsequent surgeries within a 12-month period of time. Treatment B Treatment A Surgery No Surgery Total Surgery 27 28 55 No Surgery 15 130 145 Total 42 158 200 How many participants?
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