Table 1.

Summary of intervention typology and quality appraisal

Intervention category	Intervention type	Positive effect (high bias)	No effect (high bias)	Strength of evidence
GP education	Peer review and training/feedback	4 (1)	0	i
	GP training: professional development	10 (1)	7 (2)	iii
	Guidelines (no training/feedback)	7 (2)	5	iii
	Guidelines with training/feedback/specialist support	11	6	iii
Process change	Designated appointment slots/fast-track clinic	4 (1)	2	iii
	Direct access to screening/diagnostic testing	6	3	iii
	Specialist consultation before referral	11 (3)	0	i
	Electronic referral	9 (1)	1	i
	Decision support tool	6	4	iii
	Waiting list review	1	2	iii
System change	Additional primary care staff	0	3 (1)	i (−ve)
	Community provision of ‘specialist’ services by GPs	7	2 (1)	i
	Outreach: community provision by specialists	8	2 (1)	i
	Return of inappropriate referrals	2 (1)	0	ii
	Gatekeeping	0	4 (1)	iii
	Payment system	1	3 (1)	iii
	Referral management centre	3 (2)	3	iii
Patient inventions	Patient education	1	1	iii
	Patient concerns and satisfaction	1	0	iii

i = stronger evidence. ii = weaker evidence. iii = conflicting or no evidence (evidence from one study). [–ve] = negative affect on referral outcomes. Adapted from the method of Hoogendoorn et al 1999.