Total Research, Sampling and Purposive Sampling
A population study enables you to analyse with similar intensity the whole selected population, for example, all the members of a professional association or the entire production of an artist. A population study is viable for very small populations. There are occasions when the population is so large that you would have great difficulty analysing all the observed units comprising the population. You need, therefore, to select some of the observed units for closer analysis. You can make the selection as either a random sample or as a purposive (goal-directed) sample. Your aims, the phenomena and choice of strategy all influence the researcher’s reasonable choice of sampling method.
Read more on population study, sampling and purposive sampling from the links below: