Year	Years
1970	3.22
1971	3.32
1972	3.43
1973	3.54
1974	3.66
1975	3.77
1976	3.9
1977	4.02
1978	4.15
1979	4.28
1980	4.41
1981	4.55
1982	4.69
1983	4.84
1984	4.99
1985	5.14
1986	5.29
1987	5.45
1988	5.61
1989	5.77
1990	5.94
1991	6.11
1992	6.28
1993	6.45
1994	6.63
1995	6.8
1996	6.95
1997	7.1
1998	7.26
1999	7.41
2000	7.57
2001	7.72
2002	7.88
2003	8.04
2004	8.2
2005	8.36
2006	8.52
2007	8.68
2008	8.85
2009	9.01
2010	9.17
2011	9.34
2012	9.5
2013	9.67
2014	9.83
2015	10