Year	Years
1970	2.52
1971	2.58
1972	2.64
1973	2.71
1974	2.77
1975	2.84
1976	2.9
1977	2.97
1978	3.04
1979	3.11
1980	3.18
1981	3.25
1982	3.33
1983	3.4
1984	3.48
1985	3.55
1986	3.63
1987	3.71
1988	3.79
1989	3.87
1990	3.95
1991	4.03
1992	4.11
1993	4.19
1994	4.27
1995	4.35
1996	4.43
1997	4.51
1998	4.59
1999	4.68
2000	4.76
2001	4.85
2002	4.94
2003	5.04
2004	5.13
2005	5.23
2006	5.33
2007	5.43
2008	5.53
2009	5.64
2010	5.74
2011	5.85
2012	5.96
2013	6.07
2014	6.18
2015	6.3