Year	Years
1990	57.5
1991	55.5
1992	53.6
1993	51.8
1994	50.1
1995	48.4
1996	46.8
1997	45.2
1998	43.8
1999	42.5
2000	41.3
2001	40.4
2002	39.6
2003	39
2004	38.7
2005	38.6
2006	38.7
2007	39
2008	39.2
2009	39.1
2010	38.8
2011	38.2
2012	37.4
2013	36.6