The hierarchy of the activities of daily living in the Katz index in residents of skilled nursing facilities

Abstract

Background and purpose: Nursing facility patients are a population that has not been well studied with regard to functional status and independence previously. As such, the manner in which activities of daily living (ADL) relate to one another is not well understood in this population. An understanding of ADL difficulty ordering has helped to devise systems of functional independence grading in other populations, which have value in understanding patients' global levels of independence and providing expectations regarding changes in function. This study seeks to examine the hierarchy of ADL in the nursing facility population.

Methods: Data were analyzed from the 2004 National Nursing Home Survey, a cross-sectional data set of 13 507 skilled nursing facility subjects with functional independence items. The ADL difficulty hierarchy was determined using Rasch analysis. Item fit values for the Rasch model using Mean-Square infit statistics were also determined. The robustness of the hierarchy was tested for each ADL. Two grading systems were devised from the results of the item difficulty ordering. One was based on the most difficult item that he or she could perform, and the other assigned a grade based on the least difficult item that a subject could not perform.

Results: A total of 13 113 patients were included in this analysis, the majority of whom were female and white. They had an average age of 81 years. An ordered hierarchy of ADL was found with eating being the easiest and bathing the most difficult. All items in the Katz index fit the Rasch model adequately well. The majority of patients able to perform any particular ADL were also able to perform all easier ADL. Cohen's κ for the 2 grading systems was 0.73.

Discussion: This study is the first to show the expected hierarchy of difficulty of the 6 activities of daily proposed in the Katz index in the nursing facility population. The hierarchy found in this population matches the original hierarchy found in older adults in the community and acute care settings. It is also similar to hierarchy found in the inpatient rehabilitation setting. Patients would be expected to lose or gain function based on the order of difficulty, but this remains to be confirmed.

Conclusion: Among the 6 activities of daily living tested here, their order from easiest to most difficult is eating, maintaining continence, transferring, toileting, dressing, and bathing. In addition, the index formed by these 6 items has construct validity in the nursing facility population.