1CHAPTER 2ELEMENTS OF THE SAMPLING PROBLEM2.1An adequate frame listing individuals in a city is difficult to obtain. For that reason,and because data is desired on a family basis, it would be better to sample dwellingunits. An adequate frame for dwelling units is also difficult to obtain, so a clustersampling approach could be used by sampling city blocks and then measuring waterconsumption for the families living in the sampled blocks.2.2A common way to sample trees is to divide the farm into plots and then randomly orsystematically sample plots on which trees would be counted. Unless trees are plantedaccording to a regularly spaced design, it is difficult to use the trees themselves assampling units.2.3The sampling design depends on a careful definition of the population of interest. Asit would be almost impossible to get a listing of all cars owned by residents of a city, abetter option would be to restrict the population of cars to something like “cars thatuse city parking lots on a working day” or “cars that belong to people visiting themalls on a weekend.” Then, a listing of parking lots or sections of parking lots couldserve as frames for collections of cars.2.4If the number of plants is not too large, each could serve as a stratum from whichemployees would be sampled. In this case one would need a list of employees (aframe) for each plant. If the number of plants is large, then a sample of plants(clusters of employees) could be taken and a sample of employees (or all employees)could be interviewed in each sampled plant.2.5An area as large as a state is generally broken up into smaller areas, such as countiesand farms within counties, for sampling. Each county may contain a number of farms,so there are various sampling options. Counties could be viewed as strata, with farmsbeing sampled from each. If there are many counties, one might sample counties asclusters of farms and then sample farms from each sampled county. In either of thesescenarios a list of farms by county would be needed as a frame.2.6Most polls of this type are done by telephone using random digit dialing, The statecould be stratified by regions, with dialing taking place within each of these regions.Frames may be found for selected populations by using lists of registered voters orlists of property owners, but these frames do not cover the entire population of adults.Personal interviews generally produce the highest response rate, but they areexpensive and require a list of individuals from which to sample. MailedPreview Mode
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