Psychometric evaluation of the Northwick Park Dependency Scale.

OBJECTIVE To examine the psychometric properties of the Northwick Park Dependency Scale (NPDS). DESIGN Review of existing literature and psychometric analysis in relation to other standardized measures of disability in a large neurorehabilitation cohort. SETTING A regional post-acute specialist inpatient neurorehabilitation unit in London, UK. PARTICIPANTS A total of 569 inpatients with complex neurological disabilities (350 males, 219 females; mean age 44.4 years). MAIN MEASURES The NPDS, Barthel Index, Functional Independence and Functional Assessment measures. RESULTS A database search found 5 studies that examined the psychometrics of the NPDS. These supported its validity and reliability. The present study added to these by evaluating the internal consistency, factor structure, discriminatory power and responsiveness to change during rehabilitation. The NPDS was found to have good internal consistency (α = 0.90), suggesting that it can reasonably be summed to a single total score. It discriminated among people with different levels of dependency and was responsive to change, particularly in the higher dependency groups. CONCLUSION The NPDS is a psychometrically robust tool, providing a broader range of information on nursing needs than some other commonly-used disability measures. The Special Nursing Needs subscale provides clinically useful information, but its metric properties require further development, which is now underway.