Year	Years
1970	2.24
1971	2.3
1972	2.37
1973	2.44
1974	2.51
1975	2.58
1976	2.66
1977	2.74
1978	2.82
1979	2.9
1980	2.99
1981	3.08
1982	3.17
1983	3.26
1984	3.36
1985	3.46
1986	3.57
1987	3.67
1988	3.79
1989	3.9
1990	4.02
1991	4.15
1992	4.28
1993	4.42
1994	4.56
1995	4.71
1996	4.87
1997	5.03
1998	5.2
1999	5.36
2000	5.52
2001	5.68
2002	5.84
2003	5.99
2004	6.15
2005	6.31
2006	6.46
2007	6.61
2008	6.77
2009	6.92
2010	7.07
2011	7.22
2012	7.37
2013	7.51
2014	7.66
2015	7.8