Setting and study population

The study population included all persons aged ≥18 years who were listed with a Danish GP clinic and who had at least five consecutive years of residence in Denmark (to allow for the collection of register-based data in the 5 years preceding the inclusion). Eligible persons were followed from 1 January 2016 until death, emigration, exit from the GP listing system for other reasons, or 31 December 2016, whichever came first. We excluded GP clinics accumulating less than 500 patient years in 2016 (table 1, online supplemental material 1).

Extent of selected PIMs* and any PIM† among adults in Denmark in 2016

*PIMs were identified through our coding algorithm for selected STOPP criteria. The algorithm was modified in accordance with the STOPP/START criteria as developed by O’Mahony and colleagues²⁶ and Huibers and colleagues.²⁷

†The measure ‘any PIM’ included unique individuals and unique PIM time only, which implied that individuals contributed only once with PIM time, even when having two or more concurrent PIMs. Thus, this measure estimated the time spent with at least one PIM.

‡The number of persons represented unique individuals.

§In some cases, the risk population (and their risk time of relevance) included all persons in the study population (ie, B3, C10, D5, H6 and M). Although the risk population for each of these criteria included all individuals, the criteria in which PIMs were defined by two or more concurrent treatments (ie, B3, C10 and M) had risk populations that differed slightly from the entire study population due to exclusion of individuals during the quarantine periods in-between treatments. In other cases, the risk population included only patients with a given condition or combination of conditions.

¶The PIM rate was calculated as the total time spent with PIM divided by the total time spent at risk.

NSAIDs, non-steroidal anti-inflammatory drugs; PIMs, potentially inappropriate medications.

bmjopen-2020-046756supp001.pdf

Denmark has free tax-funded healthcare, and more than 98% of the population are listed with a specific GP clinic, which serves as their primary entry point to the healthcare system and as a gatekeeper to specialised care.¹⁶ Around half of the Danish GP clinics are solo practices, around 40% of clinics consist of two–three GPs, and approximately 10% of clinics have more than three GPs.¹⁷