| Year | Value | | 2022 | 8.1605903199179 | | 2021 | 4.2227896203322 | | 2020 | 3.3986292851886 | | 2019 | 2.3775873278977 | | 2018 | 2.9676036600446 | | 2017 | 4.9759515055389 | | 2016 | 4.6646623581021 | | 2015 | 3.4027432773719 | | 2014 | 3.3050376255299 | | 2013 | 4.6316161972946 | | 2012 | 6.4412128093412 | | 2011 | 6.4293968107234 | | 2010 | 3.9765528847817 | | 2009 | 4.5615068767098 | | 2008 | 10.287684792119 | | 2007 | 5.9959075587637 | | 2006 | 6.6952646577335 | | 2005 | 7.7974978178644 | | 2004 | 4.107035939554 | | 2003 | 5.2277338613968 | | 2002 | 4.3787597178087 | | 2001 | 5.077450455225 | | 2000 | 4.1654044229028 | | 1999 | 3.8123720536602 | | 1998 | 6.4652262970863 | | 1997 | 6.8706392761615 | | 1996 | 7.1916466043334 | | 1995 | 16.433503452416 | | 1994 | 34.649636150832 | | 1993 | 7.9170741936265 | | 1992 | 9.4865425061716 | | 1991 | 8.5926476049019 | | 1990 | 6.6002256487402 | | 1989 | 8.2750160875159 | | 1988 | 9.3106365298707 | | 1987 | 8.1523425380087 | | 1986 | 6.1847785445693 |
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