Alba Ayala1, Rogelio Pujol2, Maria João Forjaz3, Antonio Abellán4. 1. Instituto de Economía, Geografía y Demografía, Centro de Ciencias Humanas y Sociales, Consejo Superior de Investigaciones Científicas, Madrid, España; Red de Investigación en Servicios de Salud en Enfermedades Crónicas (REDISSEC), España. Electronic address: arwen.alba@gmail.com. 2. Instituto Nacional de Estadística, Madrid, España. 3. Red de Investigación en Servicios de Salud en Enfermedades Crónicas (REDISSEC), España; Departamento de Epidemiología y Bioestadística, Escuela Nacional de Sanidad, Instituto de Salud Carlos III, Madrid, España. 4. Instituto de Economía, Geografía y Demografía, Centro de Ciencias Humanas y Sociales, Consejo Superior de Investigaciones Científicas, Madrid, España.
Abstract
OBJECTIVE: To compare the psychometric properties of scales top measure activities of daily living, constructed with different scaling methods, and to check whether the most complex scales have higher discriminatory capacity. METHOD: Sample of elderly people from the Spanish Survey on Disability, Personal Autonomy and Dependency We used 14 items that measured activities of daily living. Five scaling methods were applied: Sum and Rasch (both for dichotomous and polytomous items) and Guttman (dichotomous). We evaluated the discriminatory capacity (relative precision [RP]) and area under the curve (AUC). RESULTS: All methods showed high Pearson correlations among them (0.765-0.993). They had similar discriminatory power when comparing extreme categories of individuals with no disability with severely limited (RP: 0.93-1.00). The polytomous Sum procedure showed the highest AUC (0.934; 95% confidence interval [95%CI]: 0.928-0.939) and Guttman the lowest (0.853; 95%CI: 0.845-0.861). CONCLUSIONS: Polytomous items have greater reliability than the dichotomous ones. Simplest methods (Sum) and most complex (Rasch) are equally valid. Guttman method presented worse discriminatory capacity.
OBJECTIVE: To compare the psychometric properties of scales top measure activities of daily living, constructed with different scaling methods, and to check whether the most complex scales have higher discriminatory capacity. METHOD: Sample of elderly people from the Spanish Survey on Disability, Personal Autonomy and Dependency We used 14 items that measured activities of daily living. Five scaling methods were applied: Sum and Rasch (both for dichotomous and polytomous items) and Guttman (dichotomous). We evaluated the discriminatory capacity (relative precision [RP]) and area under the curve (AUC). RESULTS: All methods showed high Pearson correlations among them (0.765-0.993). They had similar discriminatory power when comparing extreme categories of individuals with no disability with severely limited (RP: 0.93-1.00). The polytomous Sum procedure showed the highest AUC (0.934; 95% confidence interval [95%CI]: 0.928-0.939) and Guttman the lowest (0.853; 95%CI: 0.845-0.861). CONCLUSIONS: Polytomous items have greater reliability than the dichotomous ones. Simplest methods (Sum) and most complex (Rasch) are equally valid. Guttman method presented worse discriminatory capacity.
Keywords:
Actividades de la vida diaria; Activities of daily living; Guttman; Métodos de escalamiento; Older people; Población mayor; Rasch; Scaling methods