Year	Years
1970	2.98
1971	3.06
1972	3.14
1973	3.23
1974	3.32
1975	3.41
1976	3.5
1977	3.59
1978	3.69
1979	3.78
1980	3.88
1981	3.97
1982	4.07
1983	4.17
1984	4.27
1985	4.37
1986	4.48
1987	4.58
1988	4.68
1989	4.79
1990	4.89
1991	5
1992	5.1
1993	5.21
1994	5.32
1995	5.43
1996	5.55
1997	5.67
1998	5.8
1999	5.93
2000	6.06
2001	6.19
2002	6.33
2003	6.47
2004	6.61
2005	6.75
2006	6.89
2007	7.04
2008	7.18
2009	7.33
2010	7.48
2011	7.64
2012	7.79
2013	7.94
2014	8.1
2015	8.26