Year	Years
1970	2.31
1971	2.36
1972	2.42
1973	2.48
1974	2.54
1975	2.6
1976	2.66
1977	2.73
1978	2.79
1979	2.85
1980	2.92
1981	2.99
1982	3.06
1983	3.13
1984	3.2
1985	3.27
1986	3.35
1987	3.42
1988	3.5
1989	3.57
1990	3.65
1991	3.73
1992	3.81
1993	3.9
1994	3.98
1995	4.07
1996	4.16
1997	4.26
1998	4.35
1999	4.45
2000	4.55
2001	4.65
2002	4.76
2003	4.86
2004	4.97
2005	5.07
2006	5.18
2007	5.29
2008	5.4
2009	5.52
2010	5.63
2011	5.75
2012	5.86
2013	5.98
2014	6.1
2015	6.22