Year	Years
1970	1.55
1971	1.62
1972	1.7
1973	1.78
1974	1.86
1975	1.94
1976	2.04
1977	2.13
1978	2.23
1979	2.34
1980	2.45
1981	2.57
1982	2.69
1983	2.82
1984	2.96
1985	3.1
1986	3.25
1987	3.41
1988	3.57
1989	3.74
1990	3.92
1991	4.1
1992	4.29
1993	4.49
1994	4.68
1995	4.88
1996	5.02
1997	5.17
1998	5.31
1999	5.46
2000	5.61
2001	5.75
2002	5.9
2003	6.05
2004	6.2
2005	6.34
2006	6.49
2007	6.64
2008	6.8
2009	6.95
2010	7.1
2011	7.26
2012	7.41
2013	7.57
2014	7.72
2015	7.88