Year	Years
1990	56.1
1991	55.7
1992	55.3
1993	54.8
1994	54.3
1995	53.9
1996	53.6
1997	53.3
1998	53.1
1999	53
2000	52.8
2001	52.8
2002	52.7
2003	52.9
2004	53.2
2005	53.6
2006	54.4
2007	55.2
2008	55.9
2009	56.5
2010	57.2
2011	57.8
2012	58.2
2013	58.9