| Year | Value | | 2021 | 71.422467278784 | | 2020 | 72.209843440294 | | 2019 | 73.894927243332 | | 2018 | 73.595552426184 | | 2017 | 73.391108227952 | | 2016 | 72.881950483488 | | 2015 | 72.572884577642 | | 2014 | 72.298432748875 | | 2013 | 72.099984346151 | | 2012 | 71.651104443046 | | 2011 | 71.219201198142 | | 2010 | 70.766421100023 | | 2009 | 70.460913633749 | | 2008 | 69.879207247386 | | 2007 | 69.553869930144 | | 2006 | 69.036285572171 | | 2005 | 68.382321901912 | | 2004 | 68.307428097504 | | 2003 | 67.958585939545 | | 2002 | 67.838875921677 | | 2001 | 67.74899300656 | | 2000 | 67.603371032065 | | 1999 | 67.485508579409 | | 1998 | 67.911786303933 | | 1997 | 67.496643629419 | | 1996 | 66.957784362808 | | 1995 | 66.308943182341 | | 1994 | 66.263035311083 | | 1993 | 66.275222032924 | | 1992 | 67.252931005523 | | 1991 | 68.323251674641 | | 1990 | 68.617260893726 | | 1989 | 68.734277287575 | | 1988 | 68.609736970869 | | 1987 | 68.631536734128 | | 1986 | 68.442449790124 | | 1985 | 67.408640197828 | | 1984 | 66.971128142507 | | 1983 | 67.075518263633 | | 1982 | 67.023559738217 | | 1981 | 66.647490836211 | | 1980 | 66.396651202504 | | 1979 | 66.156379619068 | | 1978 | 66.225944633448 | | 1977 | 66.119637639231 | | 1976 | 66.103671550637 | | 1975 | 66.118253044507 | | 1974 | 66.288902517638 | | 1973 | 66.187444716444 | | 1972 | 66.065744264535 | | 1971 | 65.977994397571 | | 1970 | 65.727262692648 | | 1969 | 65.077907349105 | | 1968 | 65.3692635206 | | 1967 | 65.312939347591 | | 1966 | 65.420293632999 | | 1965 | 65.345038286554 | | 1964 | 65.511077440188 | | 1963 | 65.019506977259 | | 1962 | 64.579496118297 | | 1961 | 64.689911405309 | | 1960 | 64.439746518137 |
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