Year	Years
1970	4.59
1971	4.69
1972	4.79
1973	4.89
1974	4.99
1975	5.1
1976	5.2
1977	5.31
1978	5.42
1979	5.53
1980	5.64
1981	5.75
1982	5.87
1983	5.98
1984	6.1
1985	6.22
1986	6.34
1987	6.46
1988	6.58
1989	6.7
1990	6.82
1991	6.94
1992	7.07
1993	7.19
1994	7.32
1995	7.45
1996	7.58
1997	7.71
1998	7.84
1999	7.97
2000	8.1
2001	8.24
2002	8.37
2003	8.51
2004	8.65
2005	8.79
2006	8.93
2007	9.06
2008	9.2
2009	9.34
2010	9.49
2011	9.63
2012	9.77
2013	9.91
2014	10.05
2015	10.19