Year	Years
1970	3.51
1971	3.6
1972	3.69
1973	3.78
1974	3.87
1975	3.97
1976	4.06
1977	4.16
1978	4.26
1979	4.36
1980	4.47
1981	4.57
1982	4.67
1983	4.78
1984	4.89
1985	5
1986	5.11
1987	5.22
1988	5.34
1989	5.46
1990	5.58
1991	5.7
1992	5.83
1993	5.96
1994	6.09
1995	6.23
1996	6.38
1997	6.54
1998	6.69
1999	6.84
2000	7
2001	7.16
2002	7.32
2003	7.47
2004	7.63
2005	7.79
2006	7.96
2007	8.12
2008	8.28
2009	8.44
2010	8.61
2011	8.77
2012	8.94
2013	9.1
2014	9.27
2015	9.43