An article from California's Alameda Times-Star, posted on a website called www.cannabisnews.com, described a study to be conducted at the San Mateo County Health Center, in which marijuana would be dispensed to 60 AIDS patients for pain management. Only those who had already used marijuana in the past would be eligible.
a. Would this be called a random sample, a systematic sample, or a convenience sample?
b. Why do you think the researchers used this type of sample?