Year	Years
1970	3.69
1971	3.8
1972	3.91
1973	4.02
1974	4.13
1975	4.24
1976	4.36
1977	4.48
1978	4.6
1979	4.72
1980	4.85
1981	4.98
1982	5.11
1983	5.24
1984	5.37
1985	5.5
1986	5.64
1987	5.78
1988	5.91
1989	6.05
1990	6.19
1991	6.33
1992	6.48
1993	6.62
1994	6.76
1995	6.9
1996	7.05
1997	7.19
1998	7.33
1999	7.48
2000	7.62
2001	7.77
2002	7.92
2003	8.07
2004	8.22
2005	8.37
2006	8.52
2007	8.67
2008	8.83
2009	8.98
2010	9.14
2011	9.29
2012	9.45
2013	9.61
2014	9.77
2015	9.93