Year	Years
1970	2.02
1971	2.09
1972	2.15
1973	2.22
1974	2.29
1975	2.36
1976	2.43
1977	2.51
1978	2.59
1979	2.67
1980	2.75
1981	2.83
1982	2.92
1983	3.01
1984	3.1
1985	3.19
1986	3.29
1987	3.38
1988	3.48
1989	3.59
1990	3.69
1991	3.8
1992	3.91
1993	4.03
1994	4.14
1995	4.26
1996	4.38
1997	4.5
1998	4.63
1999	4.75
2000	4.88
2001	5.01
2002	5.14
2003	5.28
2004	5.41
2005	5.55
2006	5.69
2007	5.83
2008	5.97
2009	6.11
2010	6.25
2011	6.4
2012	6.55
2013	6.7
2014	6.85
2015	7