Year	Years
1970	2.73
1971	2.82
1972	2.9
1973	2.99
1974	3.08
1975	3.17
1976	3.26
1977	3.36
1978	3.46
1979	3.56
1980	3.67
1981	3.78
1982	3.89
1983	4
1984	4.12
1985	4.23
1986	4.36
1987	4.48
1988	4.61
1989	4.74
1990	4.87
1991	5.01
1992	5.15
1993	5.29
1994	5.44
1995	5.59
1996	5.75
1997	5.9
1998	6.06
1999	6.22
2000	6.38
2001	6.54
2002	6.7
2003	6.86
2004	7.02
2005	7.19
2006	7.35
2007	7.52
2008	7.69
2009	7.85
2010	8.02
2011	8.19
2012	8.36
2013	8.53
2014	8.7
2015	8.87