Table 1.

Characteristics of the participating primary health care centers. Ca: circa.

Number	Organization	Number of patients (2013)	Region of the Netherlands	Remarks
1	Health care center	Ca 13,000	Mid
2	Health care center	Ca 8000	South	Located in deprived urban area
3	General practice	Ca 3500	South
4	Health care center	Ca 5000	West	Located in deprived urban area
5	General practice	Ca 5500	North	Patients mainly students
6	Health care center	Ca 14,500	Mid
7	General practice	Ca 6500	North