Year	Years
1970	1.81
1971	1.86
1972	1.92
1973	1.98
1974	2.04
1975	2.1
1976	2.17
1977	2.24
1978	2.31
1979	2.38
1980	2.46
1981	2.54
1982	2.62
1983	2.71
1984	2.8
1985	2.9
1986	3
1987	3.11
1988	3.23
1989	3.35
1990	3.47
1991	3.61
1992	3.75
1993	3.89
1994	4.05
1995	4.21
1996	4.32
1997	4.42
1998	4.53
1999	4.64
2000	4.75
2001	4.86
2002	4.97
2003	5.08
2004	5.19
2005	5.31
2006	5.42
2007	5.54
2008	5.66
2009	5.78
2010	5.9
2011	6.02
2012	6.14
2013	6.27
2014	6.39
2015	6.52