Year	Years
1970	3.69
1971	3.8
1972	3.9
1973	4.01
1974	4.12
1975	4.23
1976	4.34
1977	4.46
1978	4.57
1979	4.69
1980	4.82
1981	4.94
1982	5.07
1983	5.2
1984	5.33
1985	5.46
1986	5.59
1987	5.73
1988	5.87
1989	6.01
1990	6.15
1991	6.3
1992	6.44
1993	6.59
1994	6.74
1995	6.89
1996	7.04
1997	7.2
1998	7.35
1999	7.51
2000	7.67
2001	7.83
2002	7.99
2003	8.15
2004	8.31
2005	8.47
2006	8.64
2007	8.8
2008	8.97
2009	9.13
2010	9.3
2011	9.47
2012	9.64
2013	9.81
2014	9.97
2015	10.14