Out-of-pocket costs, primary care frequent attendance and sample selection: estimates from a longitudinal cohort design

This paper examines the effect of out-of-pocket costs on subsequent frequent attendance in primary care using data from the Personality and Total Health (PATH) Through Life Project, a representative community cohort study from Canberra, Australia. The analysis sample comprised 1197 respondents with two or more GP consultations, and uses survey data linked to administrative health service use (Medicare) data which provides data on the number of consultations and out-of-pocket costs. Respondents identified in the highest decile of GP use in a year were defined as Frequent Attenders (FAs). Logistic regression models that did not account for potential selection effects showed that out-of-pocket costs incurred during respondents' prior two consultations were significantly associated with subsequent FA status. Respondents who incurred higher costs ($15-$35; or >$35) were less likely to become FAs than those who incurred no or low (<AUS$15 per consultation) costs, with no difference evident between the no and low-cost groups. However, a counterfactual model that adjusted for factors associated with the selection into payment levels did not find an influence of payment, with only a non-significant gradient in the expected direction. Hence these findings raise doubts that price drives FA behaviour, suggesting that co-payments are unlikely to affect the number of GP consultations amongst frequent attenders.