Year	Years
1970	5.52
1971	5.64
1972	5.77
1973	5.89
1974	6.02
1975	6.14
1976	6.27
1977	6.4
1978	6.52
1979	6.65
1980	6.77
1981	6.9
1982	7.02
1983	7.15
1984	7.27
1985	7.4
1986	7.52
1987	7.64
1988	7.76
1989	7.87
1990	7.99
1991	8.1
1992	8.21
1993	8.32
1994	8.43
1995	8.53
1996	8.66
1997	8.79
1998	8.92
1999	9.06
2000	9.2
2001	9.34
2002	9.49
2003	9.63
2004	9.78
2005	9.93
2006	10.09
2007	10.24
2008	10.39
2009	10.55
2010	10.7
2011	10.86
2012	11.02
2013	11.18
2014	11.33
2015	11.49