In survey research it is very rare for all respondents in a given population to be interviewed. We usually take a sample of that population. The reason why we can do this is because a sample can give us, not necessarily the accuracy of a census (or full count), but sufficient accuracy for prediction purposes. This is true if the sample is representative of the population from which it is drawn. There are various sampling methods that can be used if we wish to obtain a representative sample. Such samples can give, depending mainly on the size of the sample, results to given levels of precision.