Year	Years
1970	67.33
1971	67.86
1972	68.54
1973	69.24
1974	69.8
1975	70.34
1976	70.88
1977	71.4
1978	72.15
1979	71.17
1980	73.1
1981	73.53
1982	73.6
1983	73.74
1984	73.47
1985	73.21
1986	72.99
1987	72.77
1988	72.55
1989	72.29
1990	72.06
1991	71.8
1992	71.69
1993	71.6
1994	71.59
1995	71.66
1996	71.74
1997	71.94
1998	72.15
1999	72.44
2000	72.92
2001	73.07
2002	73.08
2003	73.07
2004	73.31
2005	73.4
2006	73.41
2007	73.4
2008	73.46
2009	73.44
2010	73.04
2011	73
2012	72.92
2013	72.72
2014	72.7
2015	71.68
2016	73.01