Year	Years
1970	2.4
1971	2.48
1972	2.55
1973	2.63
1974	2.72
1975	2.8
1976	2.89
1977	2.98
1978	3.08
1979	3.18
1980	3.28
1981	3.39
1982	3.51
1983	3.63
1984	3.76
1985	3.89
1986	4.03
1987	4.18
1988	4.33
1989	4.5
1990	4.67
1991	4.86
1992	5.05
1993	5.26
1994	5.47
1995	5.69
1996	5.82
1997	5.95
1998	6.08
1999	6.22
2000	6.35
2001	6.48
2002	6.62
2003	6.75
2004	6.88
2005	7.02
2006	7.16
2007	7.29
2008	7.43
2009	7.57
2010	7.7
2011	7.84
2012	7.98
2013	8.12
2014	8.26
2015	8.4