Year	Years
1970	3.45
1971	3.53
1972	3.62
1973	3.7
1974	3.79
1975	3.89
1976	3.98
1977	4.08
1978	4.17
1979	4.27
1980	4.38
1981	4.48
1982	4.59
1983	4.7
1984	4.81
1985	4.92
1986	5.04
1987	5.16
1988	5.28
1989	5.41
1990	5.53
1991	5.66
1992	5.8
1993	5.93
1994	6.07
1995	6.21
1996	6.35
1997	6.49
1998	6.63
1999	6.77
2000	6.91
2001	7.05
2002	7.19
2003	7.33
2004	7.48
2005	7.62
2006	7.76
2007	7.9
2008	8.04
2009	8.19
2010	8.33
2011	8.47
2012	8.62
2013	8.76
2014	8.9
2015	9.05