BACKGROUND Delirium or confusional state is a common mental disorder in the elderly. To follow changes in symptoms over time and to evaluate the efficacy of treatment of delirium, a reliable and valid instrument for measuring degrees of delirium is essential.
METHOD An observer's rating scale with 22 items, the Confusional State Evaluation (CSE), was developed. Scores on 12 of the items were summarised to a "confusion score". Based on ratings of 71 demented and non-demented elderly patients with delirium, the interrater reliability and validity of the scale was studied.
RESULTS Agreement between two independent raters was fair to excellent (weighted kappa 0.38-0.93). The correlation between the "confusion score" of the scale and the global rating by a psychogeriatrician was good (r = 0.79).
CONCLUSIONS The CSE seems to be a reliable and valid measuring instrument which can be useful in following the course of confusion in elderly patients.