Part $2.$

What is the major difference between a sample and a

census?

What are some concerns related to convenience sampling?

To study the demographic profile of marketing research

interviewers in Ohio, a sample of interviewers was

generated using a variation of

Interviewers were initially contacted by placing classified

advertisements in the newspapers of seven major

metropolitan areas. These notices asked experienced

marketing research interviewers willing to answer $25$

questions about their job to write to the author. These

responses were increased through a referral system. Each

responding interviewer was asked for the names and

addresses of other interviewers. Eventually, this process

identified interviewers from many communities throughout

the state who had not seen the original newspaper notices.

Only $27$ percent of returned questionnaires resulted from

the classified notices; the remainder could be traced to

referrals and to referrals from referrals.