| Year | Value | | 2021 | 0.045614492375863 | | 2018 | 0.014468190649415 | | 2014 | 0.011343527383275 | | 2013 | 0.011522330276075 | | 2011 | 0.0087529267598853 | | 2010 | 0.0021886627270738 | | 2009 | 0.0042576744582109 | | 2008 | 0.0040887253398753 | | 2007 | 0.014860733695652 | | 2006 | 0.013784547522228 | | 2005 | 0.027161164473197 | | 2004 | 0.059351984244746 | | 2003 | 0.062397186454138 | | 2002 | 0.046025947127693 | | 2001 | 0.053348396409967 | | 2000 | 0.031506978795803 | | 1999 | 0.006974716652136 | | 1998 | 0.042778253091701 | | 1997 | 0.013396445476467 | | 1996 | 0.020831163420477 | | 1995 | 0.011566042100393 | | 1990 | 0.12785380343756 | | 1989 | 0.23751548038553 | | 1988 | 0.2626648543404 | | 1987 | 0.2118221519205 | | 1986 | 0.24460209496412 | | 1985 | 0.90659942994957 | | 1984 | 1.6345314607633 | | 1983 | 2.4025926198719 | | 1982 | 2.8451329870225 | | 1981 | 5.4728595411304 | | 1980 | 7.7875363448338 | | 1979 | 8.8474431210327 | | 1978 | 7.9717630853995 | | 1977 | 7.2061905529582 | | 1976 | 7.1424119663446 | | 1975 | 8.6754453911696 | | 1974 | 10.066625026025 | | 1973 | 10.616148166082 | | 1972 | 10.071942446043 |
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