Sampling

This chapter and the three that follow it are very much concerned with principles and practices associated with social survey research. Sampling principles are not exclusively concerned with survey research; for example, they are relevant to the selection of documents for content analysis (see Chapter 9). However, in this chapter the emphasis will be on sampling in connection with the selection of people who would be asked questions by interview or questionnaire. The chapter explores: • the related ideas of generalization (also known as external validity) and of a representative sample; the latter allows the researcher to generalize fi ndings from a sample to a population; • the idea of a probability sample—that is, one in which a random selection process has been employed; • the main types of probability sample: the simple random sample; the systematic sample; the stratifi ed random sample; and the multi-stage cluster sample; • the main issues involved in deciding on sample size; • different types of non-probability sample, including quota sampling, which is widely used in market research and opinion polls; • potential sources of error in survey research.