Year	Years
1970	2.17
1971	2.22
1972	2.28
1973	2.34
1974	2.41
1975	2.47
1976	2.54
1977	2.6
1978	2.67
1979	2.74
1980	2.82
1981	2.89
1982	2.97
1983	3.05
1984	3.13
1985	3.22
1986	3.3
1987	3.39
1988	3.48
1989	3.58
1990	3.67
1991	3.77
1992	3.88
1993	3.98
1994	4.09
1995	4.2
1996	4.31
1997	4.42
1998	4.54
1999	4.65
2000	4.77
2001	4.89
2002	5.01
2003	5.13
2004	5.25
2005	5.37
2006	5.49
2007	5.62
2008	5.74
2009	5.86
2010	5.99
2011	6.11
2012	6.24
2013	6.37
2014	6.49
2015	6.62