| Year | Value | | 2022 | 9.6214760848907 | | 2021 | 4.2593641754287 | | 2020 | 3.4684117795118 | | 2019 | 2.7440383159745 | | 2018 | 3.0673599605836 | | 2017 | 4.9759515055389 | | 2016 | 4.6646623581021 | | 2015 | 3.7740698202557 | | 2014 | 3.9698604516631 | | 2013 | 5.1618989858149 | | 2012 | 6.314744503152 | | 2011 | 6.4293968107234 | | 2010 | 4.6988906497623 | | 2009 | 4.3623482932572 | | 2008 | 10.659797899742 | | 2007 | 7.2541084130489 | | 2006 | 6.7399306038751 | | 2005 | 8.1695460488126 | | 2004 | 4.4749928907811 | | 2003 | 5.3023877321994 | | 2002 | 3.8957052575849 | | 2001 | 4.6037462196468 | | 2000 | 4.1654044229028 | | 1999 | 3.5988981635324 | | 1998 | 5.7533145841706 | | 1997 | 5.5722571112533 | | 1996 | 7.4113717352664 | | 1995 | 14.378808651642 | | 1994 | 32.293666856955 | | 1993 | 8.52787695688 | | 1992 | 9.5234771910899 | | 1991 | 8.8196409973388 | | 1990 | 6.8011976076257 | | 1989 | 8.0461586348732 | | 1988 | 6.9306861720652 | | 1987 | 7.0282719524595 | | 1986 | 6.8090559389513 | | 1985 | 10.423840230389 | | 1984 | 11.373322090294 | | 1983 | 11.126644122143 | | 1982 | 12.312450870773 | | 1981 | 11.33651544151 |
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