Year	Years
1970	2.24
1971	2.3
1972	2.36
1973	2.42
1974	2.49
1975	2.56
1976	2.62
1977	2.69
1978	2.77
1979	2.84
1980	2.92
1981	2.99
1982	3.07
1983	3.16
1984	3.24
1985	3.33
1986	3.41
1987	3.51
1988	3.6
1989	3.69
1990	3.79
1991	3.89
1992	3.99
1993	4.09
1994	4.2
1995	4.31
1996	4.42
1997	4.53
1998	4.65
1999	4.76
2000	4.87
2001	4.99
2002	5.11
2003	5.22
2004	5.34
2005	5.46
2006	5.58
2007	5.7
2008	5.81
2009	5.93
2010	6.05
2011	6.17
2012	6.29
2013	6.41
2014	6.54
2015	6.66