| Year | Value | | 2023 | 38.687388674666 | | 2022 | 38.757853941161 | | 2021 | 38.828319207657 | | 2020 | 38.898784474153 | | 2019 | 38.969249740649 | | 2018 | 39.039715007144 | | 2017 | 39.11018027364 | | 2016 | 39.180645540136 | | 2015 | 39.266769754742 | | 2014 | 39.271467439175 | | 2013 | 39.276165123608 | | 2012 | 39.280862808041 | | 2011 | 39.285560492474 | | 2010 | 39.290258176907 | | 2009 | 39.079841061677 | | 2008 | 38.869423946446 | | 2007 | 38.659006831216 | | 2006 | 38.448589715986 | | 2005 | 38.238172600755 | | 2004 | 38.027755485525 | | 2003 | 37.817338370295 | | 2002 | 37.606921255065 | | 2001 | 37.396504139834 | | 2000 | 37.186087024604 | | 1999 | 37.257139501654 | | 1998 | 37.328191978704 | | 1997 | 37.399244455754 | | 1996 | 37.470296932803 | | 1995 | 37.541349409853 | | 1994 | 37.612401886903 | | 1993 | 37.683454363953 | | 1992 | 37.754506841003 | | 1991 | 37.825559318053 | | 1990 | 37.896611795103 |
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