Year	Years
1970	2.08
1971	2.14
1972	2.21
1973	2.27
1974	2.34
1975	2.41
1976	2.49
1977	2.57
1978	2.65
1979	2.73
1980	2.81
1981	2.9
1982	3
1983	3.09
1984	3.19
1985	3.29
1986	3.4
1987	3.51
1988	3.63
1989	3.75
1990	3.87
1991	4
1992	4.14
1993	4.27
1994	4.42
1995	4.56
1996	4.7
1997	4.83
1998	4.96
1999	5.09
2000	5.22
2001	5.35
2002	5.47
2003	5.6
2004	5.73
2005	5.86
2006	5.99
2007	6.12
2008	6.25
2009	6.38
2010	6.51
2011	6.63
2012	6.76
2013	6.89
2014	7.02
2015	7.16