Year	Years
1970	2.08
1971	2.15
1972	2.22
1973	2.29
1974	2.36
1975	2.43
1976	2.51
1977	2.59
1978	2.67
1979	2.75
1980	2.83
1981	2.92
1982	3.01
1983	3.1
1984	3.2
1985	3.29
1986	3.39
1987	3.49
1988	3.6
1989	3.7
1990	3.81
1991	3.93
1992	4.04
1993	4.16
1994	4.28
1995	4.4
1996	4.53
1997	4.66
1998	4.79
1999	4.92
2000	5.05
2001	5.19
2002	5.32
2003	5.46
2004	5.6
2005	5.74
2006	5.88
2007	6.02
2008	6.17
2009	6.32
2010	6.46
2011	6.61
2012	6.76
2013	6.92
2014	7.07
2015	7.22