Year	Years
1970	4.99
1971	5.1
1972	5.21
1973	5.32
1974	5.43
1975	5.54
1976	5.65
1977	5.76
1978	5.87
1979	5.98
1980	6.09
1981	6.19
1982	6.3
1983	6.4
1984	6.49
1985	6.59
1986	6.68
1987	6.76
1988	6.85
1989	6.92
1990	6.99
1991	7.06
1992	7.11
1993	7.17
1994	7.21
1995	7.25
1996	7.37
1997	7.49
1998	7.61
1999	7.74
2000	7.88
2001	8.01
2002	8.15
2003	8.3
2004	8.44
2005	8.59
2006	8.74
2007	8.89
2008	9.05
2009	9.2
2010	9.36
2011	9.52
2012	9.68
2013	9.84
2014	10
2015	10.16