Year	Years
1970	5.37
1971	5.49
1972	5.6
1973	5.71
1974	5.83
1975	5.94
1976	6.06
1977	6.17
1978	6.29
1979	6.41
1980	6.52
1981	6.64
1982	6.75
1983	6.87
1984	6.99
1985	7.1
1986	7.21
1987	7.33
1988	7.44
1989	7.55
1990	7.66
1991	7.76
1992	7.86
1993	7.96
1994	8.06
1995	8.16
1996	8.24
1997	8.33
1998	8.42
1999	8.51
2000	8.6
2001	8.7
2002	8.8
2003	8.9
2004	9
2005	9.11
2006	9.21
2007	9.32
2008	9.43
2009	9.55
2010	9.66
2011	9.78
2012	9.9
2013	10.02
2014	10.15
2015	10.27