Year	Years
1970	3.66
1971	3.76
1972	3.87
1973	3.98
1974	4.09
1975	4.2
1976	4.31
1977	4.43
1978	4.55
1979	4.67
1980	4.8
1981	4.92
1982	5.05
1983	5.18
1984	5.32
1985	5.45
1986	5.59
1987	5.73
1988	5.87
1989	6.01
1990	6.16
1991	6.31
1992	6.46
1993	6.61
1994	6.76
1995	6.92
1996	7.07
1997	7.23
1998	7.39
1999	7.55
2000	7.71
2001	7.87
2002	8.03
2003	8.2
2004	8.36
2005	8.53
2006	8.69
2007	8.86
2008	9.03
2009	9.19
2010	9.36
2011	9.53
2012	9.7
2013	9.86
2014	10.03
2015	10.2