Year	Years
1970	2.12
1971	2.18
1972	2.25
1973	2.31
1974	2.38
1975	2.44
1976	2.51
1977	2.58
1978	2.66
1979	2.73
1980	2.81
1981	2.89
1982	2.97
1983	3.06
1984	3.15
1985	3.24
1986	3.33
1987	3.42
1988	3.52
1989	3.62
1990	3.73
1991	3.83
1992	3.94
1993	4.06
1994	4.17
1995	4.29
1996	4.4
1997	4.5
1998	4.61
1999	4.72
2000	4.83
2001	4.94
2002	5.05
2003	5.16
2004	5.27
2005	5.39
2006	5.5
2007	5.62
2008	5.73
2009	5.85
2010	5.97
2011	6.09
2012	6.2
2013	6.33
2014	6.45
2015	6.57