Year	Years
1970	2.17
1971	2.23
1972	2.28
1973	2.34
1974	2.39
1975	2.45
1976	2.51
1977	2.57
1978	2.63
1979	2.69
1980	2.76
1981	2.82
1982	2.89
1983	2.96
1984	3.02
1985	3.09
1986	3.16
1987	3.24
1988	3.31
1989	3.39
1990	3.46
1991	3.54
1992	3.62
1993	3.7
1994	3.78
1995	3.86
1996	3.95
1997	4.03
1998	4.12
1999	4.21
2000	4.3
2001	4.39
2002	4.49
2003	4.59
2004	4.69
2005	4.79
2006	4.89
2007	4.99
2008	5.1
2009	5.21
2010	5.31
2011	5.43
2012	5.54
2013	5.65
2014	5.77
2015	5.88