Year	Years
1970	2.14
1971	2.2
1972	2.27
1973	2.34
1974	2.4
1975	2.48
1976	2.55
1977	2.62
1978	2.7
1979	2.78
1980	2.86
1981	2.95
1982	3.03
1983	3.12
1984	3.22
1985	3.31
1986	3.41
1987	3.51
1988	3.61
1989	3.71
1990	3.82
1991	3.93
1992	4.04
1993	4.16
1994	4.27
1995	4.39
1996	4.5
1997	4.62
1998	4.73
1999	4.84
2000	4.96
2001	5.07
2002	5.19
2003	5.31
2004	5.42
2005	5.54
2006	5.66
2007	5.77
2008	5.89
2009	6.01
2010	6.13
2011	6.25
2012	6.36
2013	6.48
2014	6.6
2015	6.72