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

Abstract

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.

• Neurorehabilitation
• reliability
• responsiveness
• validity

Acknowledgements

The authors are grateful to all participating rehabilitation units who submit data to the UK-ROC and allow their data to be used. Special thanks are due to Keith Sephton (UK-ROC database manager) and Heather Williams (UK-ROC Senior Research Fellow) for their assistance with extracting and cleaning the data.

This article presents independent research funded by the National Institute for Health Research (NIHR) under its Programme Grants for Applied Research funding programme (RP-PG-0407-10185). Financial support for the preparation of this manuscript was also provided by the Dunhill Medical Trust, and the Luff Foundation.

The views expressed in this article are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health.

Professor Turner-Stokes led the development of the NPTDA and was first author on the source paper for the instrument as well as for the RCS and other scales within the UKRC dataset. However, she has no personal financial interest in any of the scales, all of which are freely available for download and use, both in clinical practice and research.

Declaration of interest

The authors report no declarations of interest.