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Introduction to Categorical Data Analysis

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CHAPTER 5 363<br />

ratio = 1.40 has CI (0.16, 2.63). CI is 1.40 ± 1.96(SE), so CI has width<br />

3.92(SE), and SE = 0.63.<br />

c. CI corresponds <strong>to</strong> one for log odds ratio of (0.207, 2.556); 1.38 is the midpoint<br />

of CI, suggesting it may be estimated log odds ratio, in which case<br />

exp(1.38) = 3.98 = estimated odds ratio.<br />

23. a. R = 1: logit( ˆπ) =−6.7 + 0.1A + 1.4S. R = 0: logit( ˆπ) =−7.0 + 0.1A+<br />

1.2S. YS conditional odds ratio = exp(1.4) = 4.1 for blacks and exp(1.2) =<br />

3.3 for whites. Coefficient of cross-product term, 0.22, is difference between<br />

log odds ratios 1.4 and 1.2.<br />

b. The coefficient of S of 1.2 is log odds ratio between Y and S when R = 0<br />

(whites), in which case RS interaction does not enter equation. P -value of<br />

P

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