Year | Value | 2021 | 23.233255628393 | 2020 | 22.228896968411 | 2019 | 23.29939303707 | 2018 | 24.048700669859 | 2017 | 23.898925091708 | 2016 | 23.621003162287 | 2015 | 24.128326395738 | 2014 | 24.79036194789 | 2013 | 23.580482253732 | 2012 | 23.400299278162 | 2011 | 23.214120786447 | 2010 | 23.114920195153 | 2009 | 23.24918544319 | 2008 | 46.046083217059 | 2007 | 48.563421688939 | 2006 | 41.539257935892 | 2005 | 39.58566372756 | 2004 | 37.29678065791 | 2003 | 37.614991707992 | 2002 | 36.617500719068 | 2001 | 36.385761100968 | 2000 | 35.533168166401 | 1999 | 32.20188316785 | 1998 | 31.294952611638 | 1997 | 29.246514256027 | 1996 | 30.48481956182 | 1995 | 31.498138396408 | 1994 | 35.544732049854 | 1993 | 33.244343059962 | 1992 | 30.868149094564 | 1991 | 29.01243176532 | 1990 | 30.805902838493 | 1989 | 18.357037430309 | 1988 | 17.386642193394 | 1987 | 16.331311550061 | 1986 | 16.701230847832 | 1985 | 16.556469173243 | 1984 | 16.132046321844 | 1983 | 15.405999494163 | 1982 | 14.241389544266 | 1981 | 13.793378651188 | 1980 | 14.787583573894 | 1979 | 14.199745789825 | 1978 | 13.579467401549 | 1977 | 13.230914125498 | 1976 | 12.120395779944 | 1975 | 13.389104156847 |
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