Development and validation of a chronic disability measurement instrument in Spain
Salvà A, Rivero T, Roqué M.

Cross-sectional validation study for the "Instrumento de Valoración de la Dependencia" (IVD), a questionnaire built to measure chronic disability in people over 3 years old witch will be used in Spain under the policy of a new Dependency law. Through a face-to-face interview, the instrument analyzes the difficulties and need of external help in performing a set of daily living activities, selected from the International Classification of Functioning, Disability and Health. The activities considered are eating and drinking, continence and toileting, washing, other body care, dressing, health maintenance, body transferences, and getting around both inside and outside. IVD ranges from 0 to 100, with 0 corresponding to a fully autonomous individual and 100 corresponding to a completely dependent one.

The study has been carried out in a convenience sample of 2416 Spanish disabled individuals, both institutionalized and noninstitutionalized. The sample was stratified on age group (3-17, 18-64 and over 65 years) and primary disability (mental delay, neuromuscular, osteoarticular, developmental disorders, other mental problems, internal organs and skin disorders, visual impairment, cognitive disorders, other). There were 1156 cases with mental disease or intellectual disability (MDID) and 1260 with exclusively physical disability (nonMDID). Participants were administered the IVD, the Barthel Index (BI) and an adapted version of Mini Mental State Examination.

IVD generated a broad distribution of scores (mean 37.97, standard deviation 33.10), with no signs of ceiling effect. IVD shows high internal consistency (reliability), with Cronbach's alpha values of 0.947 for the global sample, and 0.941 and 0.950 for the MDID and nonMDID subgroups, respectively. Construct validity of IVD is shown by its high and significant correlation to BI, both in the whole sample (Pearson's rho -93.9, p<0.001), as well as in the MDID (rho -94.2) and non MDID subgroups (rho -93.8). IVD is able to discriminate between levels of chronic disability, and its mean values significantly decrease as the level of dependency measured with BI decreases (t-test, p<0.001). Mean IVD in the group of individuals with BI 0-15 is 89.3, in the BI 20-35 group is 70.0, in the BI 40-55 group is 50.2, in the BI 60-90 group is 24.3 and in the BI 95-100 group is 4.6.

We conclude that IVD is a reliable and valid tool to measure chronic disability. This instrument collects specific information regarding intellectual limitations to perform daily living activities, and is able to discriminate the physical and mental aspects of chronic disability.

Keywords: ICF, chronic disability, assessment tool