Development and validation of a questionnaire (FASH—Functional Assessment Scale for Acute Hamstring Injuries): to measure the severity and impact of symptoms on function and sports ability in patients with acute hamstring injuries

Objective To develop a condition-specific patient-reported outcome measure, the Functional Assessment Scale for Acute Hamstring Injuries (FASH), de novo in three languages, following distinct and rigorous methodology for content generation, analysis and validation and to assess its psychometric properties. Background To our knowledge, there is no patient-reported functional scale specific for acute hamstring injuries. Methods The development of the scale followed specific guidelines, as well as de novo construction in three languages (Greek, English and German). Item generation was accomplished by selecting three different sources of items: literature review, focus group and key informant interviews. Content analysis was conducted by an expert committee. The 21 items selected as appropriate were tested through a structured content analytic method and item-content validity coefficient, and 10 were retained for the FASH. The validation and assessment of its psychometric properties followed theConsensus-based Standards for the selection of health status Measurement Instruments (COSMIN) recommendations to ensure quality, in a convenience sample of 140 participants. Results The face validity was adequate and tested by expert committees, authors and participants. Content validity was characterised as well addressed and conducted independently by experts and through specific content validation procedures. The dimensionality analysis indicated a one-factor solution explaining the 95.8% of total variance. Known group validity was demonstrated by significant differences between patients and controls (p