| Year | Value | | 2023 | 3.8380279159103 | | 2022 | 3.8337021283238 | | 2021 | 5.5929316893017 | | 2020 | 8.2312085405006 | | 2019 | 3.8923207405128 | | 2018 | 4.1086995735517 | | 2017 | 4.5815970796525 | | 2016 | 5.1054690107681 | | 2015 | 5.4617955434395 | | 2014 | 6.2614905790753 | | 2013 | 7.3496026061537 | | 2012 | 7.9954376630486 | | 2011 | 8.8067463459394 | | 2010 | 9.4763518250852 | | 2009 | 9.1693226551693 | | 2008 | 5.8370461819156 | | 2007 | 4.7841686776488 | | 2006 | 4.8179251364224 | | 2005 | 5.2596060486409 | | 2004 | 5.7034340115047 | | 2003 | 6.1553947365534 | | 2002 | 5.9774093846468 | | 2001 | 4.9829452029576 | | 2000 | 4.2767676425615 | | 1999 | 4.5559672375251 | | 1998 | 4.8869613617769 | | 1997 | 5.4077595294297 | | 1996 | 5.8664160370655 | | 1995 | 6.0341586309321 | | 1994 | 6.5495963863152 | | 1993 | 7.3539546277157 | | 1992 | 7.876454987309 | | 1991 | 7.1637756352713 |
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