Various data sources are available for urban MSW, but methodologies and samples vary enormously, resulting in different and sometimes contradictory estimates. The two most important official data sources are the 2000 and 2008 National Surveys of Basic Sanitation, conducted by the Brazilian Institute of Geography and Statistics, and the annually updated National Sanitation Information System (SNIS), managed by the Ministry of Cities. Available data are hardly comparable, however, due to methodological difference and poor statistical bases (e.g. the SNIS relies on self-reported data from municipalities, but the number of municipalities participating is low and some of the data fed into the systems are inconsistent).