| Year | Value | | 2022 | 34.467542778415 | | 2021 | 36.751428073882 | | 2020 | 36.228746360176 | | 2019 | 34.780382326943 | | 2018 | 35.855122849376 | | 2017 | 37.01406394734 | | 2016 | 36.785225542495 | | 2015 | 36.348664684524 | | 2014 | 34.987081526997 | | 2013 | 34.849089394768 | | 2012 | 34.663786943394 | | 2011 | 34.671316676558 | | 2010 | 35.044507441794 | | 2009 | 33.281454755503 | | 2008 | 33.321905140018 | | 2007 | 33.453472607514 | | 2006 | 32.890553463484 | | 2005 | 33.765623625266 | | 2004 | 35.462260619603 | | 2003 | 32.981863271075 | | 2002 | 31.454400861146 | | 2001 | 31.937637184407 | | 2000 | 33.893581402048 | | 1999 | 35.375721389431 | | 1998 | 37.723447121906 | | 1997 | 35.913919456157 | | 1996 | 35.965810904207 | | 1995 | 37.682640300536 | | 1994 | 37.896597969124 | | 1993 | 38.197922180777 | | 1992 | 38.133504278953 | | 1991 | 39.037674046348 | | 1990 | 39.026192440653 | | 1989 | 38.719884227264 | | 1988 | 41.417357107717 | | 1987 | 39.170074058241 | | 1986 | 35.422048758275 | | 1985 | 32.040727616229 | | 1984 | 32.09500985478 | | 1983 | 30.084246651371 | | 1982 | 26.420513522185 | | 1981 | 24.51807630979 | | 1980 | 25.103065653076 | | 1979 | 30.657008916034 | | 1978 | 31.586650499911 | | 1977 | 28.550104524374 | | 1976 | 25.54352993201 |
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