Year	World Bank estimate
1999	36.2
2001	35.4
2002	34.8
2003	33
2004	37.5
2005	36
2006	29.7
2007	31.2
2008	29.2
2009	28
2010	30
2011	29.4
2012	29.6
2013	30.6
2014	31.5
2015	32.4
2016	32.5
2017	33.6