Year	Years
1970	2.99
1971	3.07
1972	3.14
1973	3.22
1974	3.3
1975	3.38
1976	3.46
1977	3.54
1978	3.62
1979	3.71
1980	3.8
1981	3.89
1982	3.98
1983	4.07
1984	4.16
1985	4.26
1986	4.36
1987	4.45
1988	4.56
1989	4.66
1990	4.76
1991	4.87
1992	4.97
1993	5.08
1994	5.19
1995	5.31
1996	5.42
1997	5.53
1998	5.64
1999	5.76
2000	5.88
2001	6
2002	6.11
2003	6.24
2004	6.36
2005	6.48
2006	6.6
2007	6.73
2008	6.86
2009	6.98
2010	7.11
2011	7.24
2012	7.37
2013	7.5
2014	7.64
2015	7.77