Year	World Bank estimate
1984	32.4
1987	30.6
1990	31.2
1993	32
1996	34.4
1998	31.1
1999	31
2000	28.5
2001	29
2002	31.7
2003	31.8
2004	32.7
2005	33
2006	34.2
2007	35.7
2008	35.1
2009	35.1
2010	36.4
2011	39.7
2012	39.6
2013	39.9
2014	39.4
2015	39.7
2016	38.6
2017	38.1