Year	Years
1970	2.63
1971	2.7
1972	2.78
1973	2.86
1974	2.95
1975	3.03
1976	3.12
1977	3.21
1978	3.3
1979	3.39
1980	3.49
1981	3.58
1982	3.68
1983	3.78
1984	3.89
1985	3.99
1986	4.1
1987	4.21
1988	4.32
1989	4.43
1990	4.55
1991	4.67
1992	4.79
1993	4.91
1994	5.04
1995	5.17
1996	5.3
1997	5.43
1998	5.57
1999	5.71
2000	5.85
2001	6
2002	6.14
2003	6.29
2004	6.44
2005	6.59
2006	6.74
2007	6.89
2008	7.04
2009	7.2
2010	7.36
2011	7.52
2012	7.67
2013	7.84
2014	8
2015	8.16