Year	Years
1970	2.22
1971	2.28
1972	2.35
1973	2.41
1974	2.48
1975	2.55
1976	2.62
1977	2.69
1978	2.76
1979	2.84
1980	2.91
1981	2.99
1982	3.07
1983	3.16
1984	3.24
1985	3.33
1986	3.42
1987	3.51
1988	3.61
1989	3.71
1990	3.81
1991	3.91
1992	4.02
1993	4.14
1994	4.25
1995	4.38
1996	4.51
1997	4.65
1998	4.78
1999	4.92
2000	5.06
2001	5.21
2002	5.35
2003	5.5
2004	5.65
2005	5.8
2006	5.95
2007	6.11
2008	6.26
2009	6.42
2010	6.58
2011	6.73
2012	6.89
2013	7.05
2014	7.21
2015	7.37