Development and content validity of a patient reported outcomes measure to assess symptoms of major depressive disorder
BACKGROUND
Although many symptoms of Major Depressive Disorder (MDD) are assessed through patient-report, there are currently no patient-reported outcome (PRO) instruments that incorporate documented evidence of patient input in PRO instrument development. A review of existing PROs used in MDD suggested the need to conduct qualitative research with patients with MDD to better understand their experience of MDD and develop an evaluative instrument with content validity. The aim of this study was to develop a disease-specific questionnaire to assess symptoms important and relevant to adult MDD patients.


METHODS
The questionnaire development involved qualitative interviews for concept elicitation, instrument development, and cognitive interviews to support content validity. For concept elicitation, ten MDD severity-specific focus group interviews with thirty-eight patients having clinician-confirmed diagnoses of MDD were conducted in January 2009. A semi-structured discussion guide was used to elicit patients' spontaneous descriptions of MDD symptoms. Verbatim transcripts of focus groups were coded and analyzed to develop a conceptual framework to describe MDD. A PRO instrument was developed by operationalizing concepts elicited in the conceptual framework. Cognitive interviews were carried out in patients (n = 20) to refine and test the content validity of the instrument in terms of item relevance and comprehension, instructions, recall period, and response categories.


RESULTS
Concept elicitation focus groups identified thirty-five unique concepts falling into several domains: i) emotional, ii) cognitive, iii) motivation, iv) work, v) sleep, vi) appetite, vii) social, viii) activities of daily living, ix) tired/fatigue, x) body pain, and xi) suicidality. Concept saturation, the point at which no new relevant information emerges in later interviews, was achieved for each of the concepts. Based on the qualitative findings, the PRO instrument developed had 15 daily and 20 weekly items. The cognitive interviews confirmed that the instructions, item content, and response scales were understood by the patients.


CONCLUSIONS
Rigorous qualitative research resulted in the development of a PRO measure for MDD with supported content validity. The MDD PRO can assist in understanding and assessing MDD symptoms from patients' perspectives as well as evaluating treatment benefit of new targeted therapies.