In cases where external validity is not of critical importance to the study's goals or purpose, researchers might prefer to use nonprobability sampling.
[1][2] While probabilistic methods are suitable for large-scale studies concerned with representativeness, nonprobability approaches may be more suitable for in-depth qualitative research in which the focus is often to understand complex social phenomena.
[3] The in-depth analysis of a small purposive sample or case study enables the discovery and identification of patterns and causal mechanisms that do not draw time and context-free assumptions.
Nonprobability sampling is often not appropriate in statistical quantitative research.
The statistical model used can also render the data a nonprobability sample.