Assessing and demonstrating data saturation in qualitative inquiry supporting patient-reported outcomes research

In the patient-reported outcomes (PROs) field, strict regulatory requirements must be met for qualitative research that contributes to labeling claims for medicinal products. These requirements not only emphasize the importance of reaching saturation but also of providing documentary evidence that saturation has been reached. This paper reviews qualitative literature for useful definitions of the concept and for practical approaches for assessing saturation. The paper considers approaches in light of the rigorous regulatory requirements for PRO research that are used to support labeling claims for medicinal products and the wider requirements for flexibility and creativity in qualitative research in general. This assessment is facilitated by the use of examples from our past qualitative PRO studies. Based on conclusions from this assessment, we offer preliminary recommendations for future qualitative PRO studies for assessing and documenting saturation.