| Year | Value | | 2021 | 7.1023842418437 | | 2020 | 6.405400186345 | | 2019 | 7.0627224213654 | | 2018 | 6.8879868370583 | | 2017 | 7.0022069271445 | | 2016 | 6.5057379138132 | | 2015 | 7.2610997319838 | | 2014 | 7.0599060194368 | | 2013 | 8.2349712762159 | | 2012 | 10.314760129292 | | 2011 | 10.131616138002 | | 2010 | 10.011878255422 | | 2009 | 11.321332559502 | | 2008 | 13.293268285403 | | 2007 | 11.492493587717 | | 1999 | 17.122542262207 | | 1998 | 17.244936234058 | | 1997 | 13.624848551603 | | 1996 | 12.86077143194 | | 1995 | 42.02385653067 | | 1994 | 38.37328748454 | | 1993 | 41.186791121407 | | 1992 | 17.287678508258 | | 1991 | 31.925792461922 | | 1990 | 17.928710844628 |
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