What is the reason for the solidarity of the health insurance system between high and low incomes in France?

Summary This article analyzes the solidarity provided by the French health insurance system using a new tool that measures transfers between income groups through health care consumption and financing, applied to the Inès-Omar 2012 microsimulation model. The solidarity index is broken down according to the sources of financing (compulsory and supplementary insurance, out-of-pocket expenses) and discussed in terms of equity principles. Solidarity is less a matter of horizontal equity in the consumption of health care than of vertical equity in financing, guaranteed by the progressivity of compulsory insurance. Social inequalities in health care largely explain the importance of transfers received from public insurance by the poorest, even if barriers to access to care limit the solidarity of the system.