Year	Years
1970	2.93
1971	3
1972	3.08
1973	3.15
1974	3.23
1975	3.31
1976	3.39
1977	3.47
1978	3.55
1979	3.64
1980	3.72
1981	3.81
1982	3.9
1983	3.99
1984	4.09
1985	4.18
1986	4.28
1987	4.37
1988	4.47
1989	4.57
1990	4.67
1991	4.78
1992	4.88
1993	4.99
1994	5.1
1995	5.2
1996	5.31
1997	5.42
1998	5.53
1999	5.64
2000	5.76
2001	5.87
2002	5.98
2003	6.1
2004	6.22
2005	6.34
2006	6.45
2007	6.57
2008	6.7
2009	6.82
2010	6.94
2011	7.06
2012	7.19
2013	7.31
2014	7.44
2015	7.57