Table 1. Inclusion and exclusion criteria of the screening process of the yielded articles.

Inclusion criteria		Exclusion criteria
Titles	- Included the words ‘multimorbidity’ or ‘comorbidity’ or related words (see step 1 and 2 in Appendix S2)	- No data of disease combinations (or impossible to calculate prevalence rates)
	Titles not including these words were excluded	- Age of at least half of the study population was ≤ 55 years
		- Diagnosis of a disease was based on medication prescription (ATC codes) only
Abstracts	- Evidence that multimorbidity/comorbidity was the outcome variable, or the central independent variable	- Study size less than 500 persons†
	- Availability of a list of diseases to account for multimorbidity/comorbidity, morbidity indices or measures.	- Study conducted in a hospital setting‡
	Abstracts not meeting these criteria were excluded.	- Study examined solely two diseases§
		- Study was focused on an index-disease with a prevalence < 0.5% in the total population in the Netherlands
Full-texts	- Availability of prevalence rates of specific disease clusters*	- Study with a non-empiric research type: ‘letter’, ‘(narrative) review’, ‘editorial’, ‘case-study’, ‘presentation’, ‘commentary’

* or results that allowed the calculation of a prevalence rate: Some studies reported odds ratios instead of prevalence rates. These data were converted into prevalence rates. If not possible, the article was excluded.

^† to include studies with results based on solid, robust data

^‡ our study is more focused on primary care as health professionals in primary care often see patients with multiple health conditions

^§ we assumed that studies solely focusing on two diseases would provide insufficient disease clusters with applicable prevalence rates