If you can get it, the first thing you need for a good sample is a good sampling frame. (I say, ‘‘If you can get it,’’ because a lot of social research is done on populations for which no sampling frame exists. More on this at the end of this chapter.) A sampling frame is a list of units of analysis from which you take a sample and to which you generalize.
A sampling frame may be a telephone directory, or the tax rolls of a community, or a census of a community that you do yourself. In the United States, the city directories (published by R. L. Polk and Company) are available for many towns and cities at the local library or Chamber of Commerce. Professional survey researchers in the United States often purchase samples from firms that keep up-to-date databases just for this purpose.
For many projects, though, especially projects that involve field research, you have to get your own census of the population you are studying. Whether you work in a village or a hospital, a census gives you a sampling frame from which to take many samples during a research project. It also gives you a basis for comparison if you go back to the same community later.