Scaling the Spanish version of the Nottingham Health Profile: Evidence of limited value of item weights

The Nottingham Health Profile (NHP) is a measure of health status developed in Great Britain and adapted into Spanish. The objective of the study was to obtain item weights for the Spanish version and to compare them with those of the original instrument, to further assess the cross cultural equivalence of the new version. The usefulness of using weights in obtaining scores for the Spanish version was also evaluated. Weights for the Spanish items were obtained using Thurstone's method of paired comparisons in a sample of 1123 individuals, Correlations between Spanish and English weights ranged from 0.72 to 0.93. A comparison between unweighted, weighted, and randomly weighted NHP scores was also performed. Results showed extremely high correlations between these scoring strategies, and a similar precision for discriminating different levels of health status. Scaling assumptions for NHP scales were consistently satisfied using unweighted scores. Item weights comparison provided evidence of the cross cultural equivalence of the adapted version. Nevertheless, the unweighted NHP scoring is recommended because weighted NHP items do not improve the psychometric properties of the instrument.