Population definition

The researcher needs to be sure who exactly the population is. because this the larger group of people of whom the smaller group will be representative. It may be the population of the UK, the adult population of Preston, students registered at UCL. The population need not be made up of individuals - the unit may instead be businesses, e.g. all the exporting firms in a particular country.

Sampling frame selection

This is a list of the defined population and may be used to extract those people/firms/households who will make up the sample. Finding a suitable sampling frame may cause difficulties, but it is essential if a probability method of sampling is chosen. The sampling frame must be all-inclusive, i.e. every unit of the population must be on it, and be exclusive to the population under study. A telephone directory is a commonly used sampling frame, but the researcher should be aware of its imperfections.