A total of 2452 American adults responded to a survey about their income class and their general health level. Table 24 summarizes their responses.

a. What proportion of the lower-income adults have excellent health?
b. What proportion of the middle-income adults have excellent health?
c. What proportion of the upper-income adults have excellent health?
d. On the basis of finding the results for parts (a), (b), and (c), a student concludes that an increase in income causes an increase in health. Describe two problems with the student€™s logic.
e. To form the sample, the researchers randomly selected some landline-telephone users and randomly selected some cell-phone users. What type of sampling method is this?

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Table 24 Income Class versus General Health Level Health in General Total Excellent Good Poor Upper Income 223 228 5502 Middle Income Lower Income Total 412 127 762 1088 602 2452 592 283 1287 268 268 663