The Northwick Park Therapy Dependency Assessment scale: a psychometric analysis from a large multicentre neurorehabilitation dataset

PURPOSE To assess the internal reliability, construct and concurrent validity and responsiveness of the Northwick Park Therapy Dependency Assessment (NPTDA) scale. METHOD A cohort of 2505 neurorehabilitation patients submitted to the UK Rehabilitation Outcomes Collaborative database. Cronbach's coefficient-α was used to assess internal reliability and factor analysis (FA) to assess construct validity. We compared NPTDA scores at admission and discharge to determine responsiveness. RESULTS Coefficient-α for the whole scale was 0.74. The exploratory FA resulted in a four-factor model (Physical, Psychosocial, Discharge planning and Activities) that accounted for 43% of variance. This model was further supported by the confirmatory FA. The final model had a good fit: root-mean-square error of approximation of 0.069, comparative fit index/Tucker-Lewis index of 0.739/0.701 and the goodness of fit index of 0.909. The NPTDA scores at admission and discharge were significantly different for each of the factors. Expected correlations were seen between the admission scores for the NPTDA, the Rehabilitation Complexity Scale (r = 0.30, p < 0.01) and the Functional Independence Measure (r = -0.25, p < 0.01). CONCLUSIONS The scale demonstrated acceptable internal reliability and good construct and concurrent validity. NPTDA may be used to describe and quantify changes in therapy inputs in the course of a rehabilitation programme. Implications for Rehabilitation The Northwick Park Therapy Dependency Assessment (NPTDA) is designed as a measure therapy intervention, which reflects both quantitative and qualitative aspects of the inputs provided (including staff time and the different types of intervention) during inpatient rehabilitation. The scale demonstrated acceptable internal reliability and good construct and concurrent validity. NPTDA is responsive to change in the therapy inputs provided during neurorehabilitation between admission and discharge.