Year	Years
1970	4.59
1971	4.69
1972	4.79
1973	4.9
1974	5
1975	5.11
1976	5.22
1977	5.33
1978	5.44
1979	5.55
1980	5.66
1981	5.78
1982	5.89
1983	6.01
1984	6.13
1985	6.25
1986	6.37
1987	6.5
1988	6.62
1989	6.75
1990	6.87
1991	7
1992	7.13
1993	7.26
1994	7.39
1995	7.52
1996	7.65
1997	7.79
1998	7.92
1999	8.05
2000	8.19
2001	8.33
2002	8.46
2003	8.6
2004	8.74
2005	8.88
2006	9.02
2007	9.15
2008	9.29
2009	9.43
2010	9.57
2011	9.71
2012	9.86
2013	10
2014	10.14
2015	10.28