Year	Years
1970	2.28
1971	2.34
1972	2.4
1973	2.46
1974	2.52
1975	2.59
1976	2.65
1977	2.72
1978	2.78
1979	2.85
1980	2.92
1981	2.99
1982	3.07
1983	3.14
1984	3.22
1985	3.3
1986	3.38
1987	3.46
1988	3.54
1989	3.62
1990	3.7
1991	3.79
1992	3.88
1993	3.97
1994	4.06
1995	4.15
1996	4.24
1997	4.33
1998	4.42
1999	4.51
2000	4.61
2001	4.7
2002	4.8
2003	4.9
2004	5
2005	5.1
2006	5.2
2007	5.31
2008	5.41
2009	5.52
2010	5.63
2011	5.74
2012	5.85
2013	5.97
2014	6.08
2015	6.2