Year	Years
1970	1.96
1971	2.04
1972	2.13
1973	2.21
1974	2.31
1975	2.4
1976	2.5
1977	2.61
1978	2.72
1979	2.84
1980	2.97
1981	3.1
1982	3.24
1983	3.38
1984	3.54
1985	3.7
1986	3.87
1987	4.04
1988	4.23
1989	4.42
1990	4.62
1991	4.82
1992	5.03
1993	5.25
1994	5.47
1995	5.68
1996	5.84
1997	6
1998	6.15
1999	6.3
2000	6.46
2001	6.61
2002	6.76
2003	6.9
2004	7.05
2005	7.2
2006	7.35
2007	7.5
2008	7.64
2009	7.79
2010	7.93
2011	8.08
2012	8.22
2013	8.37
2014	8.51
2015	8.65