Year	Years
1970	2.21
1971	2.27
1972	2.34
1973	2.41
1974	2.49
1975	2.56
1976	2.64
1977	2.71
1978	2.79
1979	2.88
1980	2.96
1981	3.05
1982	3.13
1983	3.22
1984	3.32
1985	3.41
1986	3.51
1987	3.6
1988	3.7
1989	3.81
1990	3.91
1991	4.02
1992	4.13
1993	4.24
1994	4.35
1995	4.47
1996	4.58
1997	4.7
1998	4.83
1999	4.95
2000	5.08
2001	5.21
2002	5.34
2003	5.47
2004	5.6
2005	5.74
2006	5.88
2007	6.02
2008	6.16
2009	6.31
2010	6.45
2011	6.6
2012	6.75
2013	6.9
2014	7.05
2015	7.21