McAlister and colleagues are to be congratulated on an important study.1 They concluded that “a province-wide program to promote team-based primary care is a feasible and effective way to reduce use of emergency departments,” which suggests a causal association between primary care networks and reductions in the use of emergency departments. Their study was cross-sectional, and, although it controlled for a number of relevant factors, it did not examine pre-existing patterns of use of emergency departments.
In a study published in 2009,2 our group found substantial differences in the use of emergency departments between physician payment models in Ontario; however, on examination of an earlier time period before the models were implemented, we found the patterns to be pre-existing. Self-selection of physicians into particular models of care appears to involve important differences in physician and patient characteristics, some of which may not be measurable using existing data.3
Without a longitudinal design that accounts for baseline patterns of care, conclusions about causation may not be warranted.
Footnotes
Competing interests: None declared.