Will the real physician retirees please stand up?

Policy makers and health workforce planners rely on counts of practice licences as a measure of the size of the active physician workforce. We use a population-based approach to correlate estimates of retirement from clinical care based on these data with those produced using physician payment data. We find that licensure data generates per-capita estimates of physician supply in British Columbia that are substantially higher than activity-based estimates. Licensure data are unlikely to produce reliable estimates of the timing and extent of physician retirement and therefore should not be used as the primary basis for estimating current or future physician supply.