THE MEASUREMENT OF INSTRUMENTAL ADL - CONTENT VALIDITY AND CONSTRUCT-VALIDITY

A new measure of Instrumental Activities of Daily Living (IADL), which is able to discriminate among the large group of elderly who do not d epend on help, was tested for content validity and construct validity. Most assessments of functional ability include Physical ADL (PADL) an d Instrumental ADL (IADL). PADL-scales assess the basic capacity of pe rsons to care for themselves. IADL-scales are used to assess somewhat higher levels of performance, such as the ability to perform household chores or go shopping. Data were collected from 734 70-year-old peopl e in Denmark in the county of Copenhagen. The measure of Instrumental ADL included 30 activities in relation to tiredness and reduced speed. Construct validity was tested by the Rasch model for item analysis; i nternal validity was specifically addressed by assessing the homogenei ty of items under different conditions. The Rasch item analysis of IAD L showed that 14 items could be combined into two qualitatively differ ent additive scales. The IADL-measure complies with demands for conten t validity, distinguishes between what the elderly actually do, and wh at they are capable of doing, and is a good discriminator among the gr oup of elderly persons who do not depend on help. It is also possible to add the items in a valid way. However, to obtain valid IADL-scales, we omitted items that were highly relevant to especially elderly wome n, such as house-work items. We conclude that the criteria employed fo r this IADL-measure are somewhat contradictory.