Table 1.

Characteristics of included studies

Study and year	Study design	Country	Participants	Age, years	Condition	Intervention
Phillips et al (2004)13	Observational	US	13 534	>18	Cancer screening	Gatekeeping plan
Mitchell and Keenan (2008)14	Observational	UK	209	14–99	Surgical admission	GP referral
Vedsted and Olesen (2011)15	Ecological	19 European countries	19 countries	N/A	Cancer	Gatekeeping plan
Hartzell et al (2013)16	Observational	US	200	N/A	Suspected hand surgical condition	Gatekeeping plan
Ferris et al (2002)17	Controlled before-and-after	US	59 952	<18	N/A	Gatekeeping plan
Pati et al (2005)2	Observational	US	8195	18–65	N/A	Managed care with gatekeeping plan
Ferris et al (2001)18	Controlled before-and-after	US	59 997	>18	N/A	Without gatekeeping plan
Escarce et al (2001)19	Observational	US	55 954	18–64	N/A	HMO with gatekeeping plan
Tye et al (2004)20	Observational	US	2909	>40	Patients without a history of breast cancer	Gatekeeping plan
Linden et al (2003)21	Observational	The Netherlands and Germany	1140	15–65	Suspected psychological problems	Gatekeeping plan
Ferris et al (2001)22	Observational	US	1839	<18	N/A	Gatekeeping plan
Velasco Garrido et al (2011)4	Systematic review	Germany	26 studies	N/A	N/A	Gatekeeping plan
Haggstrom et al (2004)23	Observational	US	2623	18–65	Mammography and cervical screening	Gatekeeping plan
Joyce et al (2000)24	Observational	US	53 011	18–64	N/A	HMO with gatekeeping plan
Schneider et al (2016)25	Observational	Germany	3 616 510	≥18	N/A	Coordinated care with gatekeeping plan
Kroneman et al (2006)26	Observational	18 European countries	18 countries	N/A	N/A	Gatekeeping plan
Pati et al (2003)27	Observational	US	3254	<18	N/A	Gatekeeping plan
Delnoij et al (2000)28	Observational	18 OECD member countries	18 countries	N/A	N/A	Gatekeeping plan
Schwenkglenks et al (2006)29	Observational	Switzerland	1810	≥18	N/A	Gatekeeping plan
Kapur et al (2000)30	Observational	US	55 954	18–64	Co-payment requirement	HMO with gatekeeping plan
Rask et al (1999)31	Observational	US	1414	≥30	Patients with chest pain who were referred or self-referred to a cardiologist	Gatekeeping plan
Schillinger et al (2000)32	Randomised controlled trial	US	2293	Adult	Required to have at least one visit to PCPs within 12 months and at least one visit to any San Francisco general hospital clinic within 6 months	Required gatekeeper
Halm et al (1997)33	Observational	US	330	N/A	N/A	Gatekeeping plan
Forrest et al (2002)34	Observational	US	19 415	18–64	N/A	Primary care authorisation for referral
Franco et al (1997)35	Observational	US	4766	0–13	Visited emergency department and been triaged by a triage nurse or PCP	Primary care gatekeeper for emergency department

HMO = health maintenance organisation. N/A = not available. OECD = Organisation for Economic Co-operation and Development. PCP = primary care physician.