Year	World Bank estimate
1980	40.8
1986	42.8
1987	45.3
1991	46.8
1992	45.5
1993	44.9
1994	45.9
1995	48.9
1996	49.5
1997	49.1
1998	50.7
1999	49.8
2000	51.1
2001	53.3
2002	53.8
2003	51.2
2004	48.6
2005	48
2006	46.7
2007	46.6
2008	45.3
2009	44.1
2010	44.5
2011	42.7
2012	41.4
2013	41
2014	41.7
2016	42
2017	41.2