Year	World Bank estimate
1987	56.2
1990	57.2
1992	54.8
1994	56.4
1996	54.9
1998	55.5
2000	52.8
2003	51.5
2006	48.2
2009	49
2011	47.6
2013	47.3
2015	47.7
2017	46.6