Year	Years
1970	1.96
1971	2.02
1972	2.07
1973	2.13
1974	2.19
1975	2.25
1976	2.31
1977	2.38
1978	2.44
1979	2.51
1980	2.58
1981	2.65
1982	2.73
1983	2.8
1984	2.88
1985	2.95
1986	3.03
1987	3.11
1988	3.2
1989	3.28
1990	3.37
1991	3.45
1992	3.54
1993	3.63
1994	3.72
1995	3.81
1996	3.89
1997	3.97
1998	4.05
1999	4.13
2000	4.22
2001	4.3
2002	4.39
2003	4.47
2004	4.56
2005	4.65
2006	4.74
2007	4.83
2008	4.93
2009	5.02
2010	5.12
2011	5.21
2012	5.31
2013	5.41
2014	5.51
2015	5.61