The ADL-staircase: further validation.

The aim was to psychometrically evaluate the activities of daily living (ADL)-staircase in various age groups. This age stratified, cross-sectional study comprised 826 individuals aged 18-102 years. The factor structure was assessed by means of hierarchical cluster analyses, plots and analyses of nonclassifiable responses. Reliability was assessed in terms of internal consistency. In general, the cluster analysis revealed two main clusters, which followed the intended factor structure (i.e. grouping the items according to personal ADL and instrumental ADL) and which were found in four of the six age groups (18-29, 30-44, 45-59 and 75-89 years). Plots confirmed that, in general, the instrument followed the hierarchical structure. Acceptable Cronbach's alpha was found in the total sample, the 18-29 age group and those aged 60 years and older. The ADL-staircase showed a varying degree of acceptable construct validity and reliability. The instrument, however, seems to be more suitable for older people.