Year	Years
1970	1.5
1971	1.54
1972	1.59
1973	1.64
1974	1.7
1975	1.75
1976	1.8
1977	1.86
1978	1.92
1979	1.98
1980	2.04
1981	2.1
1982	2.16
1983	2.23
1984	2.3
1985	2.37
1986	2.44
1987	2.51
1988	2.59
1989	2.66
1990	2.74
1991	2.82
1992	2.9
1993	2.99
1994	3.07
1995	3.16
1996	3.25
1997	3.34
1998	3.44
1999	3.53
2000	3.63
2001	3.73
2002	3.83
2003	3.94
2004	4.04
2005	4.15
2006	4.26
2007	4.38
2008	4.49
2009	4.61
2010	4.73
2011	4.85
2012	4.98
2013	5.1
2014	5.23
2015	5.36