Purposive sampling is an acceptable kind of sampling for special situations. It uses the judgment of an expert in selecting cases, or selects cases with a specific purpose in mind.
With Purposive sampling, the researcher never knows whether the cases selected represent the population.
Purposive sampling is appropriate in three situations.
1. a researcher uses it to select unique cases that are especially informative.
2. a researcher may use Purposive sampling to select members of a difficult to reach, specialized population.