Year	Years
1970	3.59
1971	3.69
1972	3.79
1973	3.9
1974	4.01
1975	4.12
1976	4.23
1977	4.34
1978	4.46
1979	4.58
1980	4.7
1981	4.82
1982	4.94
1983	5.07
1984	5.2
1985	5.33
1986	5.47
1987	5.6
1988	5.74
1989	5.88
1990	6.02
1991	6.17
1992	6.31
1993	6.46
1994	6.61
1995	6.76
1996	6.91
1997	7.06
1998	7.22
1999	7.38
2000	7.54
2001	7.7
2002	7.86
2003	8.02
2004	8.18
2005	8.35
2006	8.51
2007	8.68
2008	8.84
2009	9.01
2010	9.18
2011	9.34
2012	9.51
2013	9.68
2014	9.85
2015	10.01