Gottfries' Cognitive Scale for Staff Proxy Rating of Cognitive Function Among Nursing Home Residents.

For research purposes, there is a need for tools to assess an individual's level of cognitive function. For survey-based investigations in nursing home contexts, proxy ratings allow the assessment also of individuals with severe cognitive impairment. The aim of this study was to describe the feasibility and psychometric properties of Gottfries' cognitive scale when used in a nursing home context for proxy rating of cognitive function. The psychometric properties of Gottfries' cognitive scale were investigated in a sample of 8,492 nursing home residents in Västerbotten County, Sweden, using item response theory and classic scale theory-based approaches. Cognitive function could be scored in 97.1% of the assessed individuals. The scale had a negligible floor effect, it had items with a large spread in difficulties, it appeared linear, and it distributed the assessed individuals equally over the scale. Internal consistency (Cronbach's alpha) was 0.967, and an exploratory factor analysis revealed three factors of the scale - interpreted to represent orientation to time, to place, and to person. Gottfries' cognitive scale is a feasible tool for grading cognitive function among nursing home residents using staff proxy ratings. The scale has excellent psychometric properties with a very high internal consistency, a favorable distribution of item difficulties producing an almost rectangular distribution of scores, and a negligible floor effect. The scale thus can be recommended for use in survey-based investigations in nursing home contexts.