Year	Years
1970	2.06
1971	2.13
1972	2.2
1973	2.27
1974	2.34
1975	2.42
1976	2.5
1977	2.58
1978	2.66
1979	2.75
1980	2.83
1981	2.92
1982	3.02
1983	3.11
1984	3.21
1985	3.32
1986	3.42
1987	3.53
1988	3.64
1989	3.76
1990	3.87
1991	3.99
1992	4.12
1993	4.25
1994	4.38
1995	4.51
1996	4.63
1997	4.76
1998	4.89
1999	5.02
2000	5.16
2001	5.29
2002	5.43
2003	5.57
2004	5.71
2005	5.85
2006	5.99
2007	6.14
2008	6.28
2009	6.43
2010	6.58
2011	6.74
2012	6.89
2013	7.05
2014	7.2
2015	7.36