According to the 1991 census, Bosnia and Herzegovina had a population of 4,369,319, while the 1996 World Bank Group census showed a decrease to 3,764,425. Large population migrations during the Yugoslav Wars in the 1990s have caused demographic shifts in the country. Between 1991 and 2013, political disagreements made it impossible to organize a census. A census had been planned for 2011, and then for 2012, but was delayed until October 2013. The 2013 census found a total population of 3,531,159 people, a drop of approximately 20% since 1991. The 2013 census figures include non-permanent Bosnian residents and for this reason are contested by Republika Srpska officials and Serb politicians (see Ethnic groups below).