Measurement properties and factor analysis of the Diabetic Foot Ulcer Scale-short form (DFS-SF)

Abstract

The purpose of this paper is to provide measurement properties evaluation and factor analysis of the Brazilian version of the diabetic foot ulcer scale-short form (DFS-SF). This methodological study evaluated the measurement properties of the DFS-SF by ceiling and floor effect reliability, responsiveness, and structural construct validity. The study included 290 people with diabetic foot under regular follow-up in a specialised outpatient clinic in inland São Paulo. Reliability was assessed by internal consistency using Cronbach's alpha and composite reliability. Ceiling and floor effects were assessed by the percentage of participants who scored the 15% worst (floor) and 15% best (ceiling) possible scale results. Validity was tested by correlating the instrument values with the domains of the Brazilian version of the Short Form Health Survey (SF-36). Responsiveness (n = 34) was accessed through the wound area obtained by photography and evaluated by the Image J Features program and the DFS-SF score at two moments, with a 4-week interval between them. The instrument had good evidence of reliability, shown by adequate internal consistency (Cronbach's alpha in domains >0.70) and compound reliability (0.84 > CC > 0.92); and of convergent validity, by significant positive correlations of moderate to strong magnitude with SF-36. Structural construct validity was examined by applying the DFS-SF confirmatory factor analysis, which indicated that the Brazilian version of the instrument is properly fitted to the original dimensional structure. The ceiling and floor effect analysis showed no ceiling or floor effects. Responsiveness was observed in the wound area, but not in the DFS-SF scores in the times. The Brazilian version of the DFS-SF presented evidence of validity and reliability, suggesting that this instrument is a valid tool for assessing the quality of life of people with diabetic foot in the Brazilian population.

Keywords: diabetes mellitus; nursing; quality of life; questionnaires; validation studies.