Year	Years
1970	1.88
1971	1.94
1972	2
1973	2.07
1974	2.13
1975	2.2
1976	2.27
1977	2.34
1978	2.42
1979	2.5
1980	2.57
1981	2.66
1982	2.74
1983	2.83
1984	2.92
1985	3.01
1986	3.1
1987	3.2
1988	3.3
1989	3.4
1990	3.5
1991	3.61
1992	3.72
1993	3.83
1994	3.95
1995	4.07
1996	4.19
1997	4.31
1998	4.43
1999	4.55
2000	4.68
2001	4.8
2002	4.93
2003	5.06
2004	5.19
2005	5.33
2006	5.46
2007	5.6
2008	5.74
2009	5.88
2010	6.02
2011	6.17
2012	6.31
2013	6.46
2014	6.61
2015	6.76