The measurement of multimorbidity.

The presence of multiple concurrent medical conditions (also known as multimorbidity) is now a common phenomenon, hence the importance of its measurement.The purpose of this paper is to review the multimorbidity measures that have been published in the literature to date and that are available for use in future research studies.Two main groups of measures of multimorbidity could be distinguished. The first group of measures is constituted by a simple count from various lists of chronic conditions. The second group of measures introduces a weighting for included chronic conditions thus creating a "weighted index" of multimorbidity. These groups are not mutually exclusive as the list of medical conditions in some weighted indices can be used as a list of conditions without weighting. This article includes a review of the multimorbidity literature to date that has reported these groups of measurements, showing the variety of existing measurements and highlighting their differences to provide an overview of the possibilities that are available to a researcher intending to measure multimorbidity.Finally, we outline some guidelines for the choice of a measurement of multimorbidity for research studies. We hope that this review of the existing literature will help inform the careful use of these tools by researchers moving forward. In addition to this review, it is advised that readers attempt to keep updated on the ever-increasing multimorbidity literature. (PsycINFO Database Record (c) 2019 APA, all rights reserved).