Year	Years
1970	4.69
1971	4.79
1972	4.89
1973	4.99
1974	5.1
1975	5.21
1976	5.31
1977	5.42
1978	5.54
1979	5.65
1980	5.76
1981	5.88
1982	5.99
1983	6.11
1984	6.23
1985	6.35
1986	6.47
1987	6.59
1988	6.71
1989	6.84
1990	6.96
1991	7.09
1992	7.22
1993	7.34
1994	7.47
1995	7.6
1996	7.73
1997	7.86
1998	7.99
1999	8.12
2000	8.25
2001	8.38
2002	8.52
2003	8.65
2004	8.78
2005	8.92
2006	9.06
2007	9.19
2008	9.33
2009	9.47
2010	9.61
2011	9.74
2012	9.88
2013	10.02
2014	10.16
2015	10.3