Year	Years
1970	4.65
1971	4.75
1972	4.85
1973	4.95
1974	5.05
1975	5.16
1976	5.27
1977	5.37
1978	5.48
1979	5.59
1980	5.7
1981	5.81
1982	5.92
1983	6.04
1984	6.15
1985	6.26
1986	6.38
1987	6.49
1988	6.61
1989	6.72
1990	6.84
1991	6.96
1992	7.07
1993	7.18
1994	7.3
1995	7.41
1996	7.53
1997	7.65
1998	7.78
1999	7.9
2000	8.03
2001	8.15
2002	8.28
2003	8.41
2004	8.54
2005	8.67
2006	8.81
2007	8.94
2008	9.07
2009	9.21
2010	9.34
2011	9.48
2012	9.62
2013	9.75
2014	9.89
2015	10.03