Year	Years
1970	2.18
1971	2.24
1972	2.3
1973	2.36
1974	2.42
1975	2.49
1976	2.56
1977	2.62
1978	2.69
1979	2.76
1980	2.84
1981	2.91
1982	2.99
1983	3.07
1984	3.14
1985	3.23
1986	3.31
1987	3.39
1988	3.48
1989	3.56
1990	3.65
1991	3.74
1992	3.83
1993	3.93
1994	4.02
1995	4.11
1996	4.21
1997	4.3
1998	4.4
1999	4.49
2000	4.59
2001	4.69
2002	4.79
2003	4.89
2004	4.98
2005	5.08
2006	5.18
2007	5.29
2008	5.39
2009	5.49
2010	5.59
2011	5.69
2012	5.8
2013	5.9
2014	6.01
2015	6.12