Year	Years
1970	2.89
1971	2.98
1972	3.08
1973	3.17
1974	3.27
1975	3.37
1976	3.48
1977	3.58
1978	3.7
1979	3.81
1980	3.93
1981	4.05
1982	4.17
1983	4.3
1984	4.43
1985	4.57
1986	4.7
1987	4.85
1988	4.99
1989	5.14
1990	5.29
1991	5.45
1992	5.61
1993	5.78
1994	5.95
1995	6.12
1996	6.29
1997	6.45
1998	6.62
1999	6.79
2000	6.97
2001	7.14
2002	7.31
2003	7.48
2004	7.66
2005	7.83
2006	8
2007	8.18
2008	8.35
2009	8.53
2010	8.7
2011	8.87
2012	9.05
2013	9.22
2014	9.39
2015	9.56