Year	Years
1970	4.5
1971	4.6
1972	4.69
1973	4.79
1974	4.89
1975	4.99
1976	5.1
1977	5.2
1978	5.31
1979	5.41
1980	5.52
1981	5.63
1982	5.73
1983	5.84
1984	5.96
1985	6.07
1986	6.18
1987	6.29
1988	6.41
1989	6.52
1990	6.64
1991	6.75
1992	6.87
1993	6.99
1994	7.11
1995	7.23
1996	7.35
1997	7.47
1998	7.6
1999	7.72
2000	7.85
2001	7.98
2002	8.11
2003	8.24
2004	8.37
2005	8.51
2006	8.64
2007	8.78
2008	8.92
2009	9.06
2010	9.2
2011	9.34
2012	9.48
2013	9.62
2014	9.76
2015	9.9