Year	Years
1990	58.7
1991	58.5
1992	58.1
1993	57.7
1994	57.2
1995	56.8
1996	56.3
1997	55.9
1998	55.5
1999	55.2
2000	55
2001	54.8
2002	54.7
2003	54.7
2004	54.7
2005	55.2
2006	55.7
2007	56
2008	56.6
2009	57.1
2010	57.5
2011	57.9
2012	58.3
2013	58.7