Year	Years
1970	2.03
1971	2.1
1972	2.17
1973	2.24
1974	2.32
1975	2.4
1976	2.48
1977	2.56
1978	2.65
1979	2.74
1980	2.84
1981	2.94
1982	3.05
1983	3.16
1984	3.28
1985	3.4
1986	3.53
1987	3.66
1988	3.81
1989	3.96
1990	4.11
1991	4.28
1992	4.46
1993	4.64
1994	4.83
1995	5.03
1996	5.19
1997	5.34
1998	5.49
1999	5.64
2000	5.78
2001	5.93
2002	6.08
2003	6.22
2004	6.37
2005	6.51
2006	6.65
2007	6.8
2008	6.94
2009	7.08
2010	7.23
2011	7.37
2012	7.51
2013	7.65
2014	7.8
2015	7.94