Year	Years
1970	2.65
1971	2.73
1972	2.82
1973	2.91
1974	3
1975	3.09
1976	3.19
1977	3.29
1978	3.39
1979	3.49
1980	3.6
1981	3.71
1982	3.82
1983	3.94
1984	4.06
1985	4.18
1986	4.31
1987	4.43
1988	4.57
1989	4.7
1990	4.84
1991	4.98
1992	5.12
1993	5.26
1994	5.4
1995	5.55
1996	5.69
1997	5.82
1998	5.96
1999	6.1
2000	6.25
2001	6.39
2002	6.54
2003	6.69
2004	6.84
2005	6.99
2006	7.14
2007	7.3
2008	7.45
2009	7.61
2010	7.77
2011	7.93
2012	8.09
2013	8.26
2014	8.42
2015	8.58