Year	World Bank estimate
1996	35.4
2001	36
2002	34.8
2003	33.7
2004	31.8
2005	39.8
2006	30.2
2007	30.1
2008	28.5
2009	28.2
2010	28
2011	28
2012	28.2
2013	27.1
2014	27
2015	26.8
2016	27.2
2017	27.5