In the Bulgarian census of 2011, a total of 48,945 people declared themselves to be Roman Catholics, up from 43,811 in the previous census of 2001 though down as compared to 53,074 in 1992. The vast majority of the Catholics in Bulgaria in 2001 were ethnic Bulgarians and the rest belonged to a number of other ethnic groups such as Croatians, Italians, Arabs and Germans. Bulgarian Catholics live predominantly in the regions of Svishtov and Plovdiv and are mostly descendants of the heretical Christian sect of the Paulicians, which converted to Roman Catholicism in the 16th and 17th centuries. The largest Roman Catholic Bulgarian town is Rakovski in Plovdiv Province. Ethnic Bulgarian Roman Catholics known as the Banat Bulgarians also inhabit the Central European region of the Banat. Their number is unofficially estimated at about 12,000, although Romanian censuses count only 6,500 Banat Bulgarians in the Romanian part of the region. Bulgarian Catholics are descendants of three groups. The first were converted Paulicians from the course of the Osam river  and around Plovdiv are the second  group, while the third  one is formed by more recent Eastern Orthodox converts.
Question: How many years pass between each census?
Answer: 10