sampling

When choosing the method of sampling, we usually try to make sure that the samples represent the general population. But there are some cases where we might need an inquiry on certain items that fulfill specific criteria. This is where purposive sampling is useful. In purposive sampling, the items are selected in such manner that each of them are rich in information about the parameters that we are trying to study in the population.

Suppose you have to run a survey about the coffee drinking habits of high school students of USA. The population of the students is about 4 million. You can not even imagine running the survey by asking each and every student to get the relevant data because of requirement of huge amount of time, money and other resources. The cost of the survey in this case would be too monumental to justify the effort. To solve these types of problem, sampling can be used.