**9.8 Purposive sampling**

Pre-selected research hypotheses criteria are used to classify research subjects, such as a lung cancer study for individuals having repeated exposure to asbestos. That is where the researcher includes cases or participants in the study because they think they should be included. The purposive sampling approach may prove to be successful when only a limited number of people can serve as primary data sources due to the nature of the research design and objectives.

Purposive sampling is one of the most cost-effective and time-effective sampling methods available. The disadvantages of purposive sampling are vulnerability of errors of judgment by the researcher, poor level of reliability and high degree of bias and inability to generalize the results of study (**Figure 7**) [36].
