| Year | Value | | 2022 | 79.68 | | 2021 | 78.715 | | 2020 | 79.274 | | 2019 | 78.975 | | 2018 | 78.662 | | 2017 | 78.394 | | 2016 | 78.049 | | 2015 | 77.717 | | 2014 | 77.415 | | 2013 | 77.083 | | 2012 | 76.772 | | 2011 | 76.421 | | 2010 | 76.131 | | 2009 | 75.842 | | 2008 | 75.492 | | 2007 | 75.187 | | 2006 | 74.938 | | 2005 | 73.82 | | 2004 | 73.08 | | 2003 | 73.155 | | 2002 | 72.93 | | 2001 | 72.613 | | 2000 | 72.316 | | 1999 | 72.542 | | 1998 | 72.862 | | 1997 | 72.501 | | 1996 | 71.653 | | 1995 | 70.948 | | 1994 | 71.227 | | 1993 | 71.068 | | 1992 | 70.885 | | 1991 | 70.717 | | 1990 | 70.445 | | 1989 | 70.122 | | 1988 | 69.689 | | 1987 | 69.448 | | 1986 | 68.419 | | 1985 | 67.587 | | 1984 | 66.733 | | 1983 | 65.789 | | 1982 | 65.163 | | 1981 | 64.595 | | 1980 | 64.012 | | 1979 | 63.209 | | 1978 | 62.74 | | 1977 | 62.354 | | 1976 | 61.978 | | 1975 | 61.272 | | 1974 | 60.552 |
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