Quarterly of Educational Measurement

Abstract In qualitative studies, sample size is tied to the concept of theoretical saturation. Theoretical saturation occurs when the researcher continues sampling and collecting data until no new insights or concepts emerge. However, the required number of interviews and the assertion that saturation has been achieved remain topics of debate. Not all claims of reaching theoretical saturation can be accepted as valid. This issue is significant because it consumes more time and resources than traditional interviews while excluding interview-based approaches that demand lower research validity. Although various solutions exist—such as experience-based recommendations or rules of thumb—experts have shown growing interest in developing more objective, statistically grounded criteria. This paper examines two statistical approaches for determining sample size in qualitative research: one estimates the sample size a posteriori, while the other does so a priori. These methods will be reviewed, explained, and ultimately compared.