Year	Years
1970	4.71
1971	4.81
1972	4.91
1973	5.02
1974	5.12
1975	5.23
1976	5.34
1977	5.45
1978	5.56
1979	5.68
1980	5.79
1981	5.91
1982	6.03
1983	6.15
1984	6.27
1985	6.39
1986	6.51
1987	6.63
1988	6.76
1989	6.89
1990	7.01
1991	7.14
1992	7.27
1993	7.4
1994	7.54
1995	7.67
1996	7.8
1997	7.94
1998	8.07
1999	8.21
2000	8.34
2001	8.48
2002	8.62
2003	8.76
2004	8.9
2005	9.03
2006	9.17
2007	9.31
2008	9.45
2009	9.59
2010	9.73
2011	9.87
2012	10.01
2013	10.15
2014	10.29
2015	10.43