Year	Years
1970	3.58
1971	3.69
1972	3.8
1973	3.91
1974	4.02
1975	4.14
1976	4.26
1977	4.38
1978	4.51
1979	4.64
1980	4.77
1981	4.9
1982	5.04
1983	5.18
1984	5.32
1985	5.47
1986	5.62
1987	5.77
1988	5.92
1989	6.08
1990	6.23
1991	6.39
1992	6.56
1993	6.72
1994	6.89
1995	7.05
1996	7.21
1997	7.37
1998	7.53
1999	7.69
2000	7.85
2001	8.01
2002	8.17
2003	8.33
2004	8.5
2005	8.66
2006	8.82
2007	8.98
2008	9.15
2009	9.31
2010	9.48
2011	9.64
2012	9.81
2013	9.97
2014	10.14
2015	10.3