A seminal study conducted by scientists at the University of Illinois found evidence of improved memory and reasoning for those who took three vigorous 40-minute walks a week over six months (Newsweek, June 28-July 5, 2010). As an assistant manager working for a public health institute based in Florida, you would like to estimate the proportion of adults in Miami, Florida, who follow such a walking regimen. Discuss the sampling bias in the following strategies where people are asked if they walk regularly:
a. Randomly selected adult beachgoers in Miami.
b. Randomly selected Miami residents who are requested to disclose the information in prepaid envelopes.
c. Randomly selected Miami residents who are requested to disclose the information on the firm's website.
d. Randomly selected adult patients at all hospitals in Miami.