| Year | Value | | 2022 | 8.5181970348361 | | 2021 | 3.4593435250432 | | 2020 | 1.9403199660718 | | 2019 | 2.1617625813305 | | 2018 | 2.4744634711843 | | 2017 | 2.1772757268926 | | 2016 | 1.1092080580703 | | 2015 | 1.5579071134626 | | 2014 | 2.0446148153933 | | 2013 | 2.6822968408504 | | 2012 | 3.3160556668765 | | 2011 | 4.3707355993922 | | 2010 | 3.2977796133984 | | 2009 | 3.0416682769848 | | 2008 | 8.9559870517778 | | 2007 | 5.4387588387656 | | 2006 | 4.3655220300907 | | 2005 | 4.1429758363102 | | 2004 | 3.857303913674 | | 2003 | 3.2346481729393 | | 2002 | 2.8011550518075 | | 2001 | 4.6460444205863 | | 2000 | 4.1028098304232 | | 1999 | 3.3880075420401 | | 1998 | 5.4415255401998 | | 1997 | 5.8798310574352 | | 1996 | 7.2269148953241 | | 1995 | 8.0129244395266 | | 1994 | 11.443119644497 | | 1993 | 10.676537184071 | | 1992 | 5.8243451463791 | | 1991 | 6.9048963274276 | | 1990 | 7.6060995774389 | | 1989 | 6.1893540338235 | | 1988 | 7.1969696969695 | | 1987 | 5.7564640111814 |
|