Year	Years
1970	3.78
1971	3.88
1972	3.98
1973	4.09
1974	4.19
1975	4.3
1976	4.41
1977	4.52
1978	4.64
1979	4.76
1980	4.88
1981	5
1982	5.13
1983	5.26
1984	5.39
1985	5.52
1986	5.66
1987	5.8
1988	5.94
1989	6.09
1990	6.24
1991	6.39
1992	6.54
1993	6.69
1994	6.85
1995	7
1996	7.15
1997	7.29
1998	7.43
1999	7.57
2000	7.71
2001	7.85
2002	7.99
2003	8.13
2004	8.27
2005	8.4
2006	8.54
2007	8.68
2008	8.82
2009	8.96
2010	9.1
2011	9.23
2012	9.37
2013	9.51
2014	9.65
2015	9.78