Year	Years
1970	3.74
1971	3.82
1972	3.91
1973	4
1974	4.09
1975	4.19
1976	4.28
1977	4.38
1978	4.47
1979	4.57
1980	4.67
1981	4.78
1982	4.88
1983	4.99
1984	5.1
1985	5.21
1986	5.32
1987	5.43
1988	5.55
1989	5.67
1990	5.79
1991	5.91
1992	6.03
1993	6.15
1994	6.28
1995	6.41
1996	6.54
1997	6.66
1998	6.79
1999	6.92
2000	7.05
2001	7.19
2002	7.32
2003	7.45
2004	7.58
2005	7.72
2006	7.85
2007	7.99
2008	8.12
2009	8.26
2010	8.4
2011	8.54
2012	8.68
2013	8.82
2014	8.96
2015	9.1