Year	Years
1975	83.3
1976	79.9
1977	76.6
1978	73.5
1979	70.8
1980	68.3
1981	66.1
1982	64.3
1983	62.7
1984	61.4
1985	60.4
1986	59.6
1987	59
1988	58.4
1989	57.8
1990	57.1
1991	56.3
1992	55.2
1993	53.9
1994	52.6
1995	51.1
1996	49.3
1997	47.5
1998	45.7
1999	44
2000	42.5
2001	41.1
2002	39.8
2003	38.8
2004	37.8
2005	36.9
2006	35.9
2007	34.9
2008	34
2009	33
2010	32
2011	31.1
2012	30.1
2013	29.2