Year	Years
1970	2.99
1971	3.07
1972	3.14
1973	3.22
1974	3.31
1975	3.39
1976	3.48
1977	3.56
1978	3.65
1979	3.74
1980	3.84
1981	3.93
1982	4.03
1983	4.13
1984	4.23
1985	4.33
1986	4.44
1987	4.54
1988	4.65
1989	4.76
1990	4.88
1991	4.99
1992	5.11
1993	5.22
1994	5.34
1995	5.47
1996	5.59
1997	5.71
1998	5.83
1999	5.96
2000	6.08
2001	6.2
2002	6.33
2003	6.45
2004	6.58
2005	6.7
2006	6.83
2007	6.96
2008	7.08
2009	7.21
2010	7.34
2011	7.46
2012	7.59
2013	7.72
2014	7.84
2015	7.97