Year	Years
1970	2.96
1971	3.05
1972	3.14
1973	3.23
1974	3.33
1975	3.43
1976	3.53
1977	3.64
1978	3.75
1979	3.86
1980	3.98
1981	4.1
1982	4.23
1983	4.36
1984	4.5
1985	4.64
1986	4.79
1987	4.94
1988	5.1
1989	5.26
1990	5.43
1991	5.61
1992	5.79
1993	5.98
1994	6.18
1995	6.38
1996	6.54
1997	6.69
1998	6.84
1999	6.99
2000	7.14
2001	7.29
2002	7.43
2003	7.58
2004	7.73
2005	7.87
2006	8.02
2007	8.16
2008	8.31
2009	8.45
2010	8.59
2011	8.74
2012	8.88
2013	9.02
2014	9.17
2015	9.31