Referral Relationships between General Practitioners and Specialists: Evidence from an unregulated fee market

In referral-based systems, general practitioners (GPs) act as gatekeepers to specialist care and usually choose which specialist a patient sees. We examine whether GP–specialist referral relationships are associated with specialist fees, out-of-pocket costs, waiting times and bulk billing (zero patient payment) in Australia, where specialists set their own fees. Using linked whole-of-population administrative data on 6.3 million initial specialist consultations in orthopaedic surgery, dermatology and cardiology between July 2021 and June 2025, we estimate models with GP, specialist and patient-area fixed effects. We measure relationships by their length, the number of consecutive years a GP has referred to the same specialist, and by the concentration of a GP’s referrals, using the Herfindahl–Hirschman Index. In all three specialties, each additional year of collaboration is associated with 0.3–0.8\% higher fees, 3.9–4.5\% higher out-of-pocket costs, 1.9–4.7 days longer waits and a lower probability of bulk billing. Most of the waiting-time difference arises when a pair becomes established. Associations with referral concentration are smaller and largely attenuate once relationship length is accounted for. Providing GPs with information on fees, out-of-pocket costs and waiting times at the point of referral, and prompting periodic review of established referral pathways, could improve affordability and access while preserving continuity of care.