A volunteer sample is a kind of convenience sample in which participants select themselves to participate. One recent year, USA Today published an online poll on its Web site asking this question about U.S. college football: “Who is your pick to win the ACC conference this year?” Eight options—seven universities, including top vote-getters Virg inia Tech and Miami, as well as “Other”—were provided. 

a. Describe the typical person who might volunteer to be in this sample. Why might this sample be biased, even with respect to the population of U.S. college football fans? 

b. What is external validity? Why might external validity be limited in this sample? 

c. What other problem can you identify with this poll?