The sample of people (or other things) that you study determines the nature and validity of the findings and theory generated by your research. This chapter looks in detail at sampling from both qualitative and statistical viewpoints, and con-

siders some related issues affecting who ends up in the sample, including access and non-response. Random sampling is the foundation of most statistical theory and analyses, so this chapter also contains introductory material relating to sampling error and statistical inference, which also helps us to establish how big samples need to be to provide

accurate estimates and to allow simple hypotheses

to be tested.