Year	Years
1970	1.96
1971	2.01
1972	2.06
1973	2.12
1974	2.17
1975	2.22
1976	2.28
1977	2.34
1978	2.39
1979	2.45
1980	2.51
1981	2.57
1982	2.64
1983	2.7
1984	2.77
1985	2.83
1986	2.9
1987	2.97
1988	3.04
1989	3.11
1990	3.19
1991	3.26
1992	3.34
1993	3.42
1994	3.49
1995	3.57
1996	3.66
1997	3.74
1998	3.82
1999	3.91
2000	4
2001	4.09
2002	4.18
2003	4.27
2004	4.37
2005	4.46
2006	4.56
2007	4.66
2008	4.76
2009	4.86
2010	4.96
2011	5.07
2012	5.18
2013	5.28
2014	5.39
2015	5.51