Year	Years
1990	51.3
1991	51.4
1992	51.6
1993	51.7
1994	51.9
1995	52
1996	52.1
1997	52.2
1998	51.5
1999	51.7
2000	51.7
2001	51.5
2002	51.3
2003	51.1
2004	50.9
2005	50.9
2006	50.9
2007	51.1
2008	51.3
2009	51.7
2010	52
2011	52.2
2012	52.5
2013	52.8