Year	Years
1970	3.46
1971	3.57
1972	3.67
1973	3.78
1974	3.89
1975	4
1976	4.11
1977	4.23
1978	4.35
1979	4.47
1980	4.59
1981	4.72
1982	4.85
1983	4.98
1984	5.12
1985	5.25
1986	5.39
1987	5.54
1988	5.68
1989	5.83
1990	5.97
1991	6.12
1992	6.28
1993	6.43
1994	6.59
1995	6.75
1996	6.9
1997	7.06
1998	7.22
1999	7.37
2000	7.53
2001	7.69
2002	7.85
2003	8.02
2004	8.18
2005	8.34
2006	8.5
2007	8.67
2008	8.83
2009	9
2010	9.16
2011	9.32
2012	9.49
2013	9.65
2014	9.82
2015	9.98