Year	Years
1970	2.99
1971	3.06
1972	3.14
1973	3.22
1974	3.29
1975	3.38
1976	3.46
1977	3.54
1978	3.63
1979	3.72
1980	3.8
1981	3.9
1982	3.99
1983	4.08
1984	4.18
1985	4.28
1986	4.38
1987	4.48
1988	4.58
1989	4.69
1990	4.8
1991	4.91
1992	5.02
1993	5.13
1994	5.24
1995	5.36
1996	5.48
1997	5.59
1998	5.71
1999	5.83
2000	5.95
2001	6.08
2002	6.2
2003	6.32
2004	6.45
2005	6.57
2006	6.7
2007	6.83
2008	6.96
2009	7.08
2010	7.21
2011	7.34
2012	7.48
2013	7.61
2014	7.74
2015	7.87