Year	Years
1970	2.63
1971	2.7
1972	2.79
1973	2.87
1974	2.95
1975	3.04
1976	3.13
1977	3.22
1978	3.32
1979	3.41
1980	3.51
1981	3.61
1982	3.72
1983	3.82
1984	3.93
1985	4.04
1986	4.16
1987	4.27
1988	4.39
1989	4.51
1990	4.64
1991	4.76
1992	4.89
1993	5.02
1994	5.16
1995	5.3
1996	5.44
1997	5.59
1998	5.73
1999	5.88
2000	6.03
2001	6.19
2002	6.34
2003	6.5
2004	6.65
2005	6.81
2006	6.97
2007	7.13
2008	7.3
2009	7.46
2010	7.63
2011	7.79
2012	7.96
2013	8.12
2014	8.29
2015	8.46