Year	Years
1970	2.2
1971	2.25
1972	2.31
1973	2.37
1974	2.43
1975	2.49
1976	2.55
1977	2.62
1978	2.68
1979	2.75
1980	2.82
1981	2.89
1982	2.96
1983	3.03
1984	3.1
1985	3.18
1986	3.26
1987	3.33
1988	3.41
1989	3.49
1990	3.58
1991	3.66
1992	3.75
1993	3.83
1994	3.92
1995	4.01
1996	4.11
1997	4.2
1998	4.29
1999	4.39
2000	4.49
2001	4.59
2002	4.69
2003	4.79
2004	4.89
2005	5
2006	5.1
2007	5.21
2008	5.32
2009	5.43
2010	5.54
2011	5.65
2012	5.77
2013	5.88
2014	6
2015	6.12