| Year | Value | | 2021 | 6.4874689754875 | | 2020 | -3.3090682937263 | | 2019 | 3.2663360920619 | | 2018 | 4.2045669993631 | | 2017 | 5.4751028818971 | | 2016 | 8.1751706522351 | | 2015 | 4.5074756985116 | | 2014 | 4.8112928389999 | | 2013 | 4.7543168401489 | | 2012 | 3.9559351119149 | | 2011 | 3.9766342600407 | | 2010 | 8.516998923389 | | 2009 | 6.3379595268037 | | 2008 | 2.1193396105479 | | 2007 | 8.0375880518807 | | 2006 | 7.3003944430989 | | 2005 | 7.5739161195483 | | 2004 | 6.9471912997499 | | 2003 | 6.5312960415859 | | 2002 | 5.6934675793471 | | 2001 | 4.406618198214 | | 2000 | 2.7890344913539 | | 1999 | 3.7491803578791 | | 1998 | 5.3053664419304 | | 1997 | 3.8937916213958 | | 1996 | 7.7628118843489 | | 1995 | 3.64683147506 | | 1994 | 4.3336944879235 | | 1993 | 4.6149922279032 | | 1992 | 3.9863365412314 | | 1991 | 2.513472302628 | | 1990 | 5.1723620761753 | | 1989 | 3.7297652826447 |
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