20. AARP and Medicare (3.5) To find out what pro- portion of Americans support proposed Medicare
legislation to help pay medical costs, the AARP
conducted a survey of their members (people
over age 50 who pay membership dues). One of
the questions was: “Even if this plan won't affect
you personally either way, do you think it should
be passed so that people with low incomes or peo-
ple with high drug costs can be helped?” Of the
respondents, 75% answered yes.1
(a) Describe how undercoverage might lead to bias in
this study. Explain the likely direction of the bias.