| Year | Value | | 2022 | 0.52647269455043 | | 2021 | 0.54014192877531 | | 2020 | 0.62997187095378 | | 2019 | 0.60502008939757 | | 2018 | 0.62717222145559 | | 2017 | 0.62651006701008 | | 2016 | 0.63987667581723 | | 2015 | 0.77553737194115 | | 2014 | 0.68509195909136 | | 2013 | 0.67861421503122 | | 2012 | 0.66590355372129 | | 2011 | 0.52641133650985 | | 2010 | 0.50547267918886 | | 2009 | 0.50275100092697 | | 2008 | 0.50205837676972 | | 2007 | 0.53172621458102 | | 2006 | 0.55125599348682 | | 2005 | 0.70040406421721 | | 2004 | 0.73079327530028 | | 2003 | 0.8607374290856 | | 2002 | 0.86516558230489 | | 2001 | 0.68352452076228 | | 2000 | 0.78275144138373 | | 1999 | 0.71949282543475 | | 1998 | 0.7353621923316 | | 1997 | 0.89466983242146 | | 1996 | 0.94970491311628 | | 1995 | 1.1028203068754 | | 1994 | 1.1895004098279 | | 1993 | 2.1023255813954 | | 1992 | 2.6327532351629 | | 1991 | 4.0022157595901 | | 1981 | 4.3355911128562 | | 1980 | 3.3461804193077 | | 1979 | 3.104786545925 | | 1978 | 3.2219457323258 | | 1977 | 2.4654631403073 | | 1976 | 2.0673642695843 | | 1975 | 1.746094142814 | | 1974 | 1.4534131691462 | | 1973 | 1.4205671697016 | | 1972 | 1.8672901983789 | | 1971 | 1.5057373786324 | | 1970 | 1.5842605555965 | | 1969 | 1.3770153192954 | | 1968 | 1.4596454295109 |
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