Year	Years
1970	2.21
1971	2.26
1972	2.32
1973	2.38
1974	2.44
1975	2.51
1976	2.57
1977	2.63
1978	2.7
1979	2.77
1980	2.84
1981	2.91
1982	2.98
1983	3.06
1984	3.13
1985	3.21
1986	3.29
1987	3.37
1988	3.45
1989	3.54
1990	3.62
1991	3.71
1992	3.8
1993	3.89
1994	3.98
1995	4.07
1996	4.17
1997	4.26
1998	4.36
1999	4.46
2000	4.56
2001	4.66
2002	4.76
2003	4.86
2004	4.97
2005	5.08
2006	5.18
2007	5.29
2008	5.4
2009	5.52
2010	5.63
2011	5.74
2012	5.86
2013	5.98
2014	6.1
2015	6.22