A textbook publisher wants to determine what percentage of college professors either require or recommend that their students purchase textbook packages with supplemental materials, such as study guides, digital media, and online tools. The publisher sends out surveys by e-mail to a random sample of 320 faculty members who have registered with its Web site and have agreed to receive solicitations. The publisher reports that 80% of college professors require or recommend that their students purchase some type of textbook package.
The survey has bias.
(a) Determine the type of bias.
(b) Suggest a remedy.