Year	Years
1970	2.3
1971	2.37
1972	2.44
1973	2.52
1974	2.59
1975	2.67
1976	2.75
1977	2.82
1978	2.91
1979	2.99
1980	3.07
1981	3.16
1982	3.24
1983	3.33
1984	3.42
1985	3.51
1986	3.6
1987	3.7
1988	3.79
1989	3.89
1990	3.99
1991	4.09
1992	4.19
1993	4.29
1994	4.39
1995	4.49
1996	4.6
1997	4.71
1998	4.82
1999	4.94
2000	5.06
2001	5.18
2002	5.3
2003	5.42
2004	5.55
2005	5.68
2006	5.81
2007	5.94
2008	6.08
2009	6.22
2010	6.36
2011	6.5
2012	6.64
2013	6.79
2014	6.94
2015	7.09