Year	Years
1970	1.77
1971	1.83
1972	1.89
1973	1.95
1974	2.01
1975	2.07
1976	2.14
1977	2.2
1978	2.27
1979	2.34
1980	2.41
1981	2.49
1982	2.56
1983	2.64
1984	2.72
1985	2.8
1986	2.88
1987	2.96
1988	3.04
1989	3.13
1990	3.22
1991	3.3
1992	3.39
1993	3.48
1994	3.57
1995	3.67
1996	3.76
1997	3.85
1998	3.94
1999	4.03
2000	4.13
2001	4.23
2002	4.33
2003	4.43
2004	4.53
2005	4.64
2006	4.75
2007	4.86
2008	4.98
2009	5.1
2010	5.22
2011	5.34
2012	5.47
2013	5.6
2014	5.73
2015	5.86