Year	Years
1970	2.09
1971	2.16
1972	2.22
1973	2.29
1974	2.36
1975	2.43
1976	2.5
1977	2.58
1978	2.65
1979	2.73
1980	2.81
1981	2.9
1982	2.98
1983	3.07
1984	3.16
1985	3.25
1986	3.34
1987	3.44
1988	3.53
1989	3.63
1990	3.74
1991	3.84
1992	3.95
1993	4.05
1994	4.17
1995	4.28
1996	4.4
1997	4.52
1998	4.64
1999	4.76
2000	4.89
2001	5.01
2002	5.14
2003	5.28
2004	5.41
2005	5.55
2006	5.68
2007	5.82
2008	5.97
2009	6.11
2010	6.26
2011	6.4
2012	6.55
2013	6.7
2014	6.86
2015	7.01