Year	Years
1970	2.68
1971	2.75
1972	2.82
1973	2.89
1974	2.96
1975	3.03
1976	3.1
1977	3.18
1978	3.25
1979	3.33
1980	3.41
1981	3.49
1982	3.57
1983	3.66
1984	3.74
1985	3.83
1986	3.92
1987	4.01
1988	4.1
1989	4.19
1990	4.29
1991	4.39
1992	4.48
1993	4.58
1994	4.69
1995	4.79
1996	4.89
1997	5
1998	5.11
1999	5.22
2000	5.33
2001	5.44
2002	5.55
2003	5.66
2004	5.78
2005	5.89
2006	6.01
2007	6.13
2008	6.25
2009	6.37
2010	6.5
2011	6.62
2012	6.75
2013	6.87
2014	7
2015	7.13