Year	World Bank estimate
1979	48.7
1989	58.9
1991	58.2
1995	57.8
1997	58.2
1998	57.5
1999	56.5
2000	56.8
2001	56.9
2002	56.2
2003	55.8
2004	54.8
2005	53.8
2006	54.6
2007	52.7
2008	52.7
2009	51.8
2010	51.6
2011	51.3
2012	51.7
2013	51.5
2014	50.5
2015	50.8
2016	50.4
2017	49.9