| Year | Value | | 2023 | 41.791706346129 | | 2022 | 41.797710740597 | | 2021 | 41.809145405196 | | 2020 | 41.816959803541 | | 2019 | 41.819602946879 | | 2018 | 41.816816078583 | | 2017 | 41.82178622205 | | 2016 | 41.827532118392 | | 2015 | 41.832502261859 | | 2014 | 41.838765412951 | | 2013 | 41.844252811167 | | 2012 | 41.851291715135 | | 2011 | 42.231384257464 | | 2010 | 41.713353754685 | | 2009 | 41.975730386455 | | 2008 | 42.366322088665 | | 2007 | 41.7441240791 | | 2006 | 42.009862220499 | | 2005 | 41.503208995735 | | 2004 | 41.249623885227 | | 2003 | 40.351344707251 | | 2002 | 39.878808065141 | | 2001 | 39.281676618845 | | 2000 | 39.078088147861 | | 1999 | 37.997587695489 | | 1998 | 36.985959157296 | | 1997 | 36.519348843221 | | 1996 | 36.480187669639 | | 1995 | 35.782718366292 | | 1994 | 35.508036189738 | | 1993 | 34.46816414631 | | 1992 | 33.870503037353 | | 1991 | 34.202417215975 | | 1990 | 33.720075222955 | | 1989 | 33.380223083883 | | 1988 | 32.67012821507 | | 1987 | 32.298520098229 | | 1986 | 32.476138037999 | | 1985 | 32.08175856275 | | 1984 | 31.849062427297 | | 1983 | 31.655424066175 | | 1982 | 31.099028305545 | | 1981 | 30.764132092542 | | 1980 | 30.350124337599 | | 1979 | 30.100312524234 | | 1978 | 29.858616776528 | | 1977 | 29.671314721468 | | 1976 | 29.374477963035 |
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