Year	Years
1990	55.4
1991	55.4
1992	55.5
1993	55.5
1994	55.5
1995	55.6
1996	55.6
1997	55.6
1998	55.6
1999	55.7
2000	55.8
2001	55.9
2002	56.1
2003	56.3
2004	56.5
2005	56.9
2006	57.2
2007	57.7
2008	58
2009	58.5
2010	58.8
2011	59.1
2012	59.5
2013	60.1