Year	Years
1970	3.03
1971	3.12
1972	3.21
1973	3.31
1974	3.41
1975	3.52
1976	3.63
1977	3.74
1978	3.86
1979	3.98
1980	4.11
1981	4.25
1982	4.39
1983	4.53
1984	4.68
1985	4.84
1986	5.01
1987	5.19
1988	5.37
1989	5.57
1990	5.77
1991	5.99
1992	6.22
1993	6.46
1994	6.72
1995	7
1996	7.21
1997	7.42
1998	7.62
1999	7.82
2000	8.02
2001	8.21
2002	8.4
2003	8.59
2004	8.77
2005	8.95
2006	9.12
2007	9.29
2008	9.46
2009	9.63
2010	9.79
2011	9.96
2012	10.12
2013	10.28
2014	10.43
2015	10.59