Year	Years
1970	1.83
1971	1.9
1972	1.97
1973	2.05
1974	2.13
1975	2.21
1976	2.3
1977	2.39
1978	2.48
1979	2.57
1980	2.67
1981	2.78
1982	2.88
1983	2.99
1984	3.11
1985	3.22
1986	3.34
1987	3.47
1988	3.6
1989	3.73
1990	3.86
1991	4
1992	4.14
1993	4.28
1994	4.43
1995	4.57
1996	4.72
1997	4.86
1998	5.01
1999	5.16
2000	5.31
2001	5.46
2002	5.61
2003	5.77
2004	5.92
2005	6.08
2006	6.23
2007	6.39
2008	6.54
2009	6.7
2010	6.85
2011	7.01
2012	7.16
2013	7.32
2014	7.47
2015	7.63