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match those of the population. Obviously, even though the quotas may be achieved and the sample may
match the population percentages in terms of subsets, the sample may still not represent (reflect) the

population to which we wish to generalize.
Often interviewers, for sampling purposes, concentrate on areas where large numbers of people are
likely to be. This could bias the findings. As we noted earlier, samples taken in airports may overrepresent

high-income groups, whereas those at a bus or rail depots may overrepresent low-income groups. Samples
at either place may underrepresent those who seldom travel. Also, people who are home during the day,

and are therefore available for house-to-house interviews or telephone calls, may be quite different in
important ways from those who are not home. In this respect, quota sampling and convenience sampling
are similar. In spite of these difficulties, the quota system is widely used and will unquestionably continue

to be so for economic and logistic reasons.
We have just reviewed four sampling techniques: simple random sampling, stratified random
sampling, convenience sampling, and quota sampling. Table 7.1 presents one more example of each

technique as it relates to our TV violence study, noting the advantages and limitations of each. For the
purposes of these examples, we will define the population as all middle-school children in the Conway,
Arkansas, school district (approximately 1000 students).