Without additional interventions to encourage change in medical practice, the effects of clinical guidelines are generally limited (Effective Health Care 1994, Oxman et al 1995). A large number of additional interventions have been used to encourage the adoption of clinical guidelines including continuing medical education, dissemination of educational materials, educational outreach, local opinion leaders, audit and feedback, manual or computerised reminders, mass media campaigns, continuous quality improvement programmes (Effective Health Care 1999). All have some effect, but none are overwhelmingly successful or effective in all circumstances (Effective Health Care 1999, Davies et al 1995, Grimshaw et al 1995) It is suggested that multiple interventions may be more effective than single ones (Wensing and Grol 1994, Greco and Eisenberg 1993).