Sources of data

Religion was only surveyed in the Austrian census until 2001. From then on, the official census was replaced by the compilation of registers and religious affiliation is no longer surveyed (see the Federal Law on register counting [Registerzählungsgesetz], BGBI. I No. 33/2006, subsequently amended by BGBI. I No. 125/2009). Some religious communities publish data on their members, but this is an incomplete data source. Any statistics concerning the religious affiliation of the Austrian population published after 2001 are estimations or demographic projections based on older census data, sometimes taking into account reported membership counts, fertility rates, and migration movements.