Purpose The STOPP/START criteria are frequently applied in observational studies to assess potentially inappropriate prescribing in older adults. This study aimed to assess the applicability of the three available STOPP/START versions in two distinct data sources.

Methods To evaluate the applicability of the three versions of STOPP/START criteria, we used two observational data sources: (i) Integrated Swedish administrative health registries (ISHR) encompassing routinely collected health data and (ii) the population-based Swedish National study on Aging and Care in Kungsholmen (SNAC-K), based on health professional-led clinical assessments. The Anatomical Therapeutic Classification code (ATC) was used to categorise medications. Diseases were categorised using the international classification of diseases version 10 (ICD10).

Results The first STOPP/START version demonstrated an applicability rate of 80% in ISHR and 84% in SNAC-K. The second version demonstrated an applicability of 64% in ISHR and 74% in SNAC-K. The third version showed an applicability of 66% in ISHR and 77% in SNAC-K. Challenges in applicability included broad definitions, vague terminology, and the lack of information on disease severity, symptomatic traits, and stability of certain conditions.

Conclusion The applicability of the STOPP/START criteria in observational studies seems to have decreased in more recent versions of the tool. Population-based studies with comprehensive clinical assessments may offer higher applicability compared to studies based on administrative data. Future versions of the STOPP/START criteria should prioritise clear and unambiguous definitions to improve their applicability in research and promote result generalisability and comparability.