Year	Years
1970	5.41
1971	5.51
1972	5.6
1973	5.7
1974	5.79
1975	5.89
1976	5.98
1977	6.07
1978	6.17
1979	6.26
1980	6.35
1981	6.44
1982	6.53
1983	6.62
1984	6.71
1985	6.8
1986	6.89
1987	6.98
1988	7.07
1989	7.15
1990	7.24
1991	7.32
1992	7.4
1993	7.49
1994	7.57
1995	7.66
1996	7.77
1997	7.88
1998	8
1999	8.12
2000	8.24
2001	8.37
2002	8.49
2003	8.62
2004	8.75
2005	8.88
2006	9.01
2007	9.14
2008	9.27
2009	9.4
2010	9.53
2011	9.67
2012	9.8
2013	9.93
2014	10.07
2015	10.2