Background: The aims of this study were to develop a web-based Spanish form of the Barthel index (BI), to evaluate its psychometric properties and stability over time (test-retest), and to determine minimal detectable change (MDC) in patients with multiple sclerosis (MS).
Methods: Participants answered the BI on two forms (web-based and face-to-face interview), 7-10 days apart. The internal consistency was evaluated using Cronbach's alpha, and intraclass correlation (ICC) and kappa (κ) coefficients were used to investigate the agreement between both forms.
Results: 143 participants were included. The Spanish web-based form of the BI showed excellent agreement between both forms for each item (κ = 0.86 (0.79 to 0.92), and for total score (κ = 0.87 (0.81 to 0.93); ICC = 0.99 (0.98 to 0.99). The internal consistency was good-excellent (Cronbach's alpha = 0.89 (0.86-0.91)). The stability over time was adequate, the agreement of each item was κ = 0.63 (0.52-0.74)), and for total score (ICC = 0.97), determining a MDC95 of 12.09 points.
Conclusions: The Spanish web-based form of the BI is a valid and reliable tool to assess functionality and can be applied in both formats in patients with MS. A total score difference of more than 12 points was found to indicate a deterioration or improvement in the patient's functionality.
Keywords: activities of daily living; disability evaluation; multiple sclerosis; test-retest reliability; web-based intervention.