Year	Years
1970	5.24
1971	5.38
1972	5.53
1973	5.67
1974	5.82
1975	5.98
1976	6.13
1977	6.29
1978	6.46
1979	6.62
1980	6.79
1981	6.97
1982	7.15
1983	7.33
1984	7.51
1985	7.7
1986	7.9
1987	8.1
1988	8.3
1989	8.51
1990	8.72
1991	8.94
1992	9.17
1993	9.4
1994	9.64
1995	9.88
1996	10.13
1997	10.37
1998	10.6
1999	10.82
2000	11.05
2001	11.26
2002	11.47
2003	11.68
2004	11.88
2005	12.07
2006	12.27
2007	12.46
2008	12.64
2009	12.82
2010	13
2011	13.17
2012	13.34
2013	13.51
2014	13.67
2015	13.83