  PROs developed de novo, using the FDA guidance may involve structured patient
interviews or focus groups. Qualitative Research is a methodology for eliciting
and coding interviews and produces concepts or themes. These concepts are used
to develop items in a PRO for use as an endpoint in Clinical trials. A
convention in the field is that interviews and code/concept elicitation are
considered complete when subsequent interviews produces "no new concepts"
-termed "saturation". FDA reviewers frequently challenge PRO developers whether
there are sufficient patient interviews to confirm that saturation is achieved
after occurrence of zero new concepts. Several authors have reported that
concrete criteria are need for confirming that saturation is achieved (Francis
2010, Mason 2010, Marshall 2013). I provide statistical methodology for
confirming saturation, suitable for review by a regulatory authority. Type I
error for saturation, may occur if further interviews elicited more concepts
after first occurrence of saturation. I use published data set on code
elicitation (Guest, 2006) to demonstrate that saturation may occur more than
once in a sequence of interviews. I provide a statistical definition for
saturation in qualitative research, that addresses regulatory concerns for
PRO's developed for use as a clinical trial endpoint in a regulatory
submission.
