Selecting the sample for a research study.

Sample selection is a very important but sometimes underestimated part of a research study. Sampling theory describes two sampling domains: probability and nonprobability. Probability samples contain some type of randomization and consist of simple, stratified, systematic, cluster, and sequential types. Nonprobability samples lack randomization and consist of convenience or accidental, purposive, quota, volunteer, and expert types. The primary distinction between the two domains is that the probability sampling study findings can be generalized to the target population while the nonprobability sampling study findings can only be generalized to the institution where the sample was studied.