Year	Years
1970	69.5
1971	67.3
1972	65.1
1973	63.1
1974	61.3
1975	59.6
1976	58
1977	56.4
1978	54.8
1979	52.9
1980	50.8
1981	48.4
1982	45.9
1983	43.2
1984	40.6
1985	38.1
1986	35.8
1987	33.7
1988	31.8
1989	30.1
1990	28.5
1991	27.1
1992	25.9
1993	24.7
1994	23.6
1995	22.5
1996	21.5
1997	20.4
1998	19.4
1999	18.4
2000	17.5
2001	16.5
2002	15.7
2003	15
2004	14.3
2005	13.7
2006	13.1
2007	12.6
2008	12.2
2009	11.7
2010	11.3
2011	10.9
2012	10.6
2013	10.2