| Year | Value | | 2021 | 0.26245359578693 | | 2019 | 0.2759105975594 | | 2018 | 0.086579270344541 | | 2017 | 0.099206349206349 | | 2016 | 0.029074318430881 | | 2015 | 0.090380292461357 | | 2014 | 0.0023142791020597 | | 2013 | 0.056559753022412 | | 2012 | 0.030774641695243 | | 2011 | 0.041330403950317 | | 2010 | 0.026746311237908 | | 2009 | 0.016121974250904 | | 2008 | 0.021471793870779 | | 2007 | 0.0060273642336206 | | 2006 | 0.038561402606751 | | 2005 | 0.043679566698698 | | 2004 | 1.4315469302741 | | 2003 | 4.0065065949998 | | 2002 | 5.0758230533511 | | 2001 | 5.3757249208242 | | 2000 | 5.4188980666243 | | 1999 | 5.59947658252 | | 1998 | 6.0262745570688 | | 1997 | 9.3351008162981 | | 1996 | 11.470113085622 | | 1995 | 12.193571176263 | | 1994 | 12.828683160625 | | 1993 | 15.978718061397 | | 1992 | 21.973670127368 | | 1991 | 24.772662218993 | | 1990 | 24.052171271078 | | 1989 | 25.467052860246 | | 1988 | 26.586363898334 | | 1987 | 26.963161696419 | | 1986 | 26.397875603097 | | 1985 | 28.720456397718 | | 1984 | 30.317497103129 | | 1983 | 31.452718136135 | | 1982 | 32.406138668128 | | 1981 | 31.258793346023 | | 1980 | 29.298230009784 | | 1979 | 28.793469752879 | | 1978 | 33.250945042164 | | 1977 | 38.924615934262 | | 1976 | 27.378304917223 | | 1975 | 22.958442313281 | | 1974 | 31.277533039648 | | 1973 | 37.299253562542 | | 1972 | 40.300198244124 |
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