Which of the following sampling procedures represents non-probability sampling?
a. The researcher obtains a sample of subjects from his own patient group because they are easy to find.
b. The researcher first splits the population into different groups (or strata) and then randomly samples from each group. The researcher randomly samples from the entire population.
c. The researcher first assigns a number to all potential subjects, and then selects every 5th person in the population in order to obtain a sample of 1,500 subjects.