Year	Years
1990	53.6
1991	54.3
1992	54.1
1993	54.2
1994	53.9
1995	53.7
1996	53.3
1997	53
1998	52.7
1999	52.5
2000	52.4
2001	52.6
2002	52.7
2003	52.9
2004	53.2
2005	53.6
2006	53.7
2007	54.5
2008	54.8
2009	55.5
2010	56.2
2011	56.5
2012	56.8
2013	57.1