Who provides the information?
This chapter is concerned with sampling: the process of actually selecting those individuals whose views will be collected in the survey in order to be representative of the whole group whose views are being sought. Good sampling practice is the key to the ability of large-scale quantitative surveys to represent the views of the population being studied to a known and calculable degree of accuracy. Sampling theory has at its heart probability theory and it is on probability theory that the validity of large-scale surveys rests. If you like, it is probability theory that allows large-scale market research surveys to ‘work’. A complete understanding of sampling theory therefore demands an understanding of basic statistical probability theory. However, it is possible for an individual without a statistical background to appreciate what sampling theory is able to do and how samples are selected without necessarily getting involved in the intricacies of the statistical basis for this. Those wishing to read a statistical treatment of sampling are recommended the appropriate chapters in the books by Chisnall, and Worcester and Downham, listed in Chapter 17. This chapter will answer four questions:
What is a sample? Why use a sample? How is the sample selected? How big does the sample need to be?