Year	Years
1970	4.68
1971	4.79
1972	4.89
1973	5
1974	5.11
1975	5.22
1976	5.34
1977	5.45
1978	5.56
1979	5.68
1980	5.8
1981	5.92
1982	6.04
1983	6.16
1984	6.28
1985	6.41
1986	6.53
1987	6.66
1988	6.79
1989	6.92
1990	7.05
1991	7.18
1992	7.31
1993	7.44
1994	7.57
1995	7.7
1996	7.83
1997	7.96
1998	8.09
1999	8.22
2000	8.35
2001	8.49
2002	8.62
2003	8.75
2004	8.89
2005	9.02
2006	9.15
2007	9.29
2008	9.42
2009	9.56
2010	9.69
2011	9.83
2012	9.96
2013	10.1
2014	10.23
2015	10.37