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Introduction to Categorical Data Analysis

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PROBLEMS 267<br />

Table 8.10. <strong>Data</strong> from General Social Survey for Problem 8.2<br />

Believe in<br />

Believe in Hell<br />

Heaven Yes No<br />

Yes 833 125<br />

No 2 160<br />

8.3 Refer <strong>to</strong> the previous exercise. Estimate and interpret the odds ratio for a<br />

logistic model for the probability of a “yes” response as a function of the item<br />

(heaven or hell), using (a) the marginal model (8.3) and (b) the conditional<br />

model (8.4).<br />

8.4 Explain the following analogy: The McNemar test is <strong>to</strong> binary data as the<br />

paired difference t test is <strong>to</strong> normally distributed data.<br />

8.5 Section 8.1.1 gave the large-sample z or chi-squared McNemar test for comparing<br />

dependent proportions. The exact P -value, needed for small samples,<br />

uses the binomial distribution. For Table 8.1, consider Ha: π1+ >π+1, or<br />

equivalently, Ha: π12 >π21.<br />

a. The exact P -value is the binomial probability of at least 132 successes out<br />

of 239 trials, when the parameter is 0.50. Explain why. (Software reports<br />

P -value = 0.060.)<br />

b. For these data, how is the mid P -value (Section 1.4.5) defined in terms of<br />

binomial probabilities? (This P -value = 0.053.)<br />

c. Explain why Ha: π1+ �= π+1 has ordinary P -value = 0.120 and mid<br />

P -value = 0.106. (The large-sample McNemar test has P -value that is<br />

an approximation for the binomial mid P -value. It is also 0.106 for<br />

these data.)<br />

8.6 For Table 7.19 on opinions about measures <strong>to</strong> deal with AIDS, treat the data<br />

as matched pairs on opinion, stratified by gender.<br />

a. For females, test the equality of the true proportions supporting government<br />

action for the two items.<br />

b. Refer <strong>to</strong> (a). Construct a 90% confidence interval for the difference between<br />

the true proportions of support. Interpret.<br />

c. For females, estimate the odds ratio exp(β) for (i) marginal model (8.3),<br />

(ii) conditional model (8.4). Interpret.<br />

d. Explain how you could construct a 90% confidence interval for the difference<br />

between males and females in their differences of proportions of<br />

support for a particular item. (Hint: The gender samples are independent.)

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