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Shopping center sampling is popular because of low costs, but typical procedures are haphazard and thus generalization is difficult. In this article, procedures are described for careful sampling of shopping centers. They require probability sampling of the centers and of times and locations within centers. Finally, for unbiased estimates, data must be weighted by number of trips and imputations made for nonshoppers.
Seymour Sudman (Sat,) studied this question.