| Year | Value | | 2021 | 69.432070648924 | | 2020 | 71.613303819646 | | 2019 | 72.200458910481 | | 2018 | 71.91581675025 | | 2017 | 71.644670206476 | | 2016 | 71.250249373157 | | 2015 | 70.827181518745 | | 2014 | 70.400867505813 | | 2013 | 70.010837747029 | | 2012 | 69.510995704265 | | 2011 | 68.998755659347 | | 2010 | 68.603786013519 | | 2009 | 68.067507951062 | | 2008 | 67.759394012786 | | 2007 | 67.32334961135 | | 2006 | 66.970987285428 | | 2005 | 66.384259100132 | | 2004 | 65.901282256457 | | 2003 | 65.470715151502 | | 2002 | 64.937224773332 | | 2001 | 64.383008584289 | | 2000 | 63.883589197417 | | 1999 | 63.45717184003 | | 1998 | 62.778021035239 | | 1997 | 62.120528829483 | | 1996 | 61.493954444998 | | 1995 | 61.152424995917 | | 1994 | 60.817355605829 | | 1993 | 60.421510534592 | | 1992 | 60.163459585327 | | 1991 | 59.537268071584 | | 1990 | 59.354013481073 | | 1989 | 58.808577615206 | | 1988 | 58.399174438873 | | 1987 | 57.86166176757 | | 1986 | 57.392689997734 | | 1985 | 56.870732239554 | | 1984 | 56.400188270401 | | 1983 | 55.833458403885 | | 1982 | 55.197929983573 | | 1981 | 54.572107296202 | | 1980 | 53.891423697907 | | 1979 | 53.201984876832 | | 1978 | 52.536620308181 | | 1977 | 51.889258272327 | | 1976 | 51.258765502639 | | 1975 | 50.660263310111 | | 1974 | 49.986990514497 | | 1973 | 49.47292252447 | | 1972 | 49.011314091082 | | 1971 | 46.945338443385 | | 1970 | 47.622349958542 | | 1969 | 47.902162010351 | | 1968 | 47.492178518089 | | 1967 | 45.99855385293 | | 1966 | 45.561389015811 | | 1965 | 44.961785378899 | | 1964 | 45.837887652133 | | 1963 | 45.431696600753 | | 1962 | 45.118164640282 | | 1961 | 44.743940205732 | | 1960 | 44.428213837912 |
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