Case Study 33 Table 1.2 Number of Number People Returning Who Date PM Level Questionnaires Wheezed School/Mail 3/5/07 19.815 3 0 School 3/6/07 19.885 72 9 School 3/7/07 20.006 69 5 School 3/8/07 19.758 30 1 School 3/9/07 19.827 44 7 School 3/10/07 19.686 31 1 School 3/11/07 19.823 38 3 School 3/12/07 19.697 66 5 School 3/13/07 19.505 42 4 School 3/14/07 19.359 31 1 School 3/15/07 19.348 19 4 School 3/16/07 19.318 3 1 School 3/17/07 19.124 2 0 School 4/12/07 14.422 10 1 Mail 4/13/07 14.418 9 1 Mail 4/14/07 14.405 8 0 Mail 4/15/07 14.141 3 0 Mail 4/16/07 13.910 4 0 Mail 4/17/07 13.951 2 0 Mail 4/18/07 13.545 2 0 Mail 4/20/07 13.326 3 0 Mail 4/22/07 13.154 2 0 Mail 9. Explain why the percentage of low-exposure people with wheeze is the same as the percentage of mail-return people with wheeze. 10. As the weather gets warmer, PM goes down because wood stoves are used less. Explain how this causes the mode of response (school or mail) to be related to PM. 11. It is generally the case in epidemiologic studies that people who have symptoms are often eager to participate, while those who are unaffected are less interested. Explain how this may cause the mode of response (school or mail) to be related to the outcome. 12. Rather than send out questionnaires, the investigators could have telephoned a random sample of people over a period of days. Explain how this might have reduced the confounding.
navidi_monk_essential_statistics_1e_ch1_3
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