Year	World Bank estimate
1981	58
1982	58.4
1983	59
1984	58.4
1985	55.6
1986	58.5
1987	59.7
1988	61.4
1989	63.3
1990	60.5
1992	53.2
1993	60.1
1995	59.6
1996	59.9
1997	59.8
1998	59.6
1999	59
2001	58.4
2002	58.1
2003	57.6
2004	56.5
2005	56.3
2006	55.6
2007	54.9
2008	54
2009	53.7
2011	52.9
2012	52.7
2013	52.8
2014	51.5
2015	51.3
2016	53.7
2017	53.3