Year	Years
1970	1.73
1971	1.79
1972	1.85
1973	1.92
1974	1.98
1975	2.05
1976	2.12
1977	2.19
1978	2.27
1979	2.34
1980	2.42
1981	2.51
1982	2.59
1983	2.68
1984	2.77
1985	2.87
1986	2.97
1987	3.07
1988	3.18
1989	3.29
1990	3.4
1991	3.52
1992	3.64
1993	3.77
1994	3.9
1995	4.04
1996	4.17
1997	4.3
1998	4.43
1999	4.56
2000	4.69
2001	4.83
2002	4.97
2003	5.11
2004	5.25
2005	5.39
2006	5.53
2007	5.68
2008	5.82
2009	5.97
2010	6.12
2011	6.27
2012	6.43
2013	6.58
2014	6.74
2015	6.9