Year	Years
1970	3.85
1971	3.95
1972	4.06
1973	4.17
1974	4.28
1975	4.39
1976	4.51
1977	4.62
1978	4.74
1979	4.86
1980	4.98
1981	5.11
1982	5.23
1983	5.36
1984	5.49
1985	5.62
1986	5.75
1987	5.88
1988	6.02
1989	6.15
1990	6.29
1991	6.43
1992	6.57
1993	6.71
1994	6.86
1995	7
1996	7.14
1997	7.29
1998	7.43
1999	7.58
2000	7.73
2001	7.89
2002	8.04
2003	8.19
2004	8.35
2005	8.51
2006	8.67
2007	8.83
2008	8.99
2009	9.15
2010	9.31
2011	9.48
2012	9.64
2013	9.81
2014	9.97
2015	10.14