improbable sampling

Although the sampling method is very important in qualitative research, the issue of sample size selection is less studied and researchers usually determine their desired sample size or the researcher's theoretical saturation is the criterion. Using a systematic review technique in other articles, this article aims to summarize new materials and findings in the field of scientific sample size suitable for qualitative sampling methods and its critical evaluation. There are qualifications such as case study, ethnography, phenomenology, data foundation theory, focus group, reminder study. This study selected 27 non-random sampling methods to be used in the field of qualitative research and after introducing them, addressed the issue of selecting the minimum sample size for each method. The results of studies showed that in qualitative research methods, in addition to the fact that, like probabilistic sampling methods, a minimum sample size should be considered, much attention has been paid to the maximum number. The result of this study shows that the minimum sample size depends on the sampling method and there is no general criterion for it and the maximum sample size depends on the sampling method but does not exceed 30 unless the researcher aims to study in depth or between them. There is no big difference. In qualitative sampling, the criterion for determining the sample size is the theoretical saturation problem and like quantitative sampling methods, criteria such as sampling error and acceptance error of test hypotheses are not the basis for determining the sample size.