Reliability and validity of the Huntington's Disease Everyday Functioning (Hi-DEF): A patient-reported measure of cognitive capacity on daily functioning in Huntington's disease.

BackgroundThe Huntington's Disease (HD) Everyday Functioning (Hi-DEF) is a novel patient-reported outcome (PRO) scale developed to assess the impact of cognitive impairment on daily functioning in early HD patients.ObjectiveTo examine the psychometric properties, including reliability and validity, of the Hi-DEF. Findings from psychometric analyses using classical test theory (CTT) approach are presented here.MethodsA non-interventional validation study was conducted across nine HD Centers of Excellence across the US.ResultsPatients with HD (n = 151) were recruited: 59% were female, mean (SD) age was 47 (12) years, and mean (range) Total Functional Capacity (TFC) score was 11.4 (8-13). Excellent internal consistency reliability was observed for the Hi-DEF scale total score (Cronbach's alpha: 0.98) and across subscales (alpha range 0.87-0.96). Most targeting and scaling assumptions were met, although there were ceiling effects for three subscales. Construct validity was demonstrated by moderate to high Spearman's rank-order correlations with TFC scores (range r = -0.38 to -0.62) and known and validated measures such as the HD-PRO-TRIAD (range r = 0.75-0.90), and ability to discriminate between levels of functional impairment (TFC 13, 12-11, and 10-8;  < 0.001). Correlations with Cambridge Neuropsychological Test Automated Battery (CANTAB) cognitive performance measures were low to moderate and ranged from 0.06 to 0.38.ConclusionsThe Hi-DEF is a reliable and valid PRO scale measuring the impact of cognitive impairment on daily functioning, assessing facets of cognitive functioning in context of activities of daily living impacted in early stages of HD.