Year	Years
1990	60.5
1991	60.2
1992	60
1993	60.1
1994	59.6
1995	59.7
1996	59.8
1997	59.7
1998	59.6
1999	59.6
2000	59.6
2001	59.7
2002	59.7
2003	59.7
2004	59.7
2005	59.9
2006	60.2
2007	60.6
2008	61
2009	61.4
2010	61.8
2011	62.2
2012	62.8
2013	63.4