PURPOSE: The objective of this study was to develop and validate a patient-reported outcome instrument to comprehensively assess the consequences of inadequate sleep for use in insomnia-related studies.
METHODS: To inform item development, relevant constructs were identified through patient focus groups, literature review, and expert input. Following a translatability assessment for United States (US) English, US Spanish, and French, the draft items were refined through iterative sets of patient interviews in the United States and France. Psychometric properties were evaluated using patient responses from a validation study including 432 participants with either a diagnosis of primary insomnia or no history of insomnia.
RESULTS: Psychometric analyses supported item reduction from 38 to 26 items, yielding a unidimensional scale and preserving the original content (mood, tiredness/energy, memory/concentration, motivation, daily performance, social interaction, sexual functioning). Evidence of internal consistency (coefficient α = 0.97), convergent validity, and known-groups validity also was documented.
CONCLUSIONS: The Sleep Functional Impact Scale (SFIS) is a psychometrically sound measure targeting the impact of insomnia on patient functioning. When administered with a sleep diary, this instrument has the ability to provide a more comprehensive assessment of treatment response in clinical studies.
