Year	Years
1970	2.83
1971	2.92
1972	3.01
1973	3.1
1974	3.19
1975	3.29
1976	3.39
1977	3.49
1978	3.6
1979	3.71
1980	3.82
1981	3.93
1982	4.05
1983	4.17
1984	4.29
1985	4.41
1986	4.54
1987	4.67
1988	4.81
1989	4.95
1990	5.09
1991	5.23
1992	5.38
1993	5.54
1994	5.69
1995	5.85
1996	6
1997	6.16
1998	6.31
1999	6.47
2000	6.62
2001	6.78
2002	6.94
2003	7.1
2004	7.26
2005	7.42
2006	7.58
2007	7.74
2008	7.91
2009	8.07
2010	8.24
2011	8.4
2012	8.57
2013	8.74
2014	8.9
2015	9.07