Census data provide a count of people residing in a locality at the time of the Census. Censuses are conducted every 10 years and the latest one took place in 2011. Census data provide more accurate figures at the local level but do not give up-to-date information on population trends. (Detailed results for the next Census, which will be held in 2021, are expected to be published 1–2 years later.) For some groups, such as Romanians and Bulgarians, most of whom arrived after 2011, this will make the census data less useful than other sources, such as the Annual Population Survey. However, for other groups the Census may still be the best source of data – for example, longer-term residents whose numbers are not likely to shift dramatically over time.