| Year | Value | | 2022 | 0.68513477335856 | | 2021 | 0.58767423699368 | | 2020 | 0.39244639884061 | | 2019 | 0.51674931029531 | | 2018 | 0.63009401403895 | | 2017 | 0.61889690371649 | | 2016 | 0.53836809692055 | | 2015 | 0.95146166358237 | | 2014 | 1.1856013702071 | | 2013 | 1.3629354415382 | | 2012 | 1.9360813364581 | | 2011 | 2.0060962477805 | | 2010 | 1.7504792003477 | | 2009 | 1.6375209334837 | | 2008 | 1.6180812223881 | | 2007 | 1.5127831679659 | | 2006 | 1.4016448028711 | | 2005 | 1.2238921329635 | | 2004 | 1.284037313428 | | 2003 | 1.2911926267396 | | 2002 | 1.282150655579 | | 2001 | 1.6542921702857 | | 2000 | 1.5154982728108 | | 1999 | 1.5042263767732 | | 1998 | 1.6111538752817 | | 1997 | 1.5502831979387 | | 1996 | 1.565977364878 | | 1995 | 1.6744979542267 | | 1994 | 1.729369725171 | | 1993 | 6.3120535893582 | | 1992 | 10.317917788943 | | 1991 | 11.399728899855 | | 1990 | 10.358732959789 | | 1989 | 10.391029782073 | | 1988 | 10.545988291717 | | 1987 | 15.057204612582 | | 1986 | 15.119352242284 | | 1985 | 17.139862498795 | | 1984 | 18.829215444974 | | 1983 | 18.082013482637 | | 1982 | 19.301430143014 | | 1981 | 20.69341205827 | | 1980 | 20.112754642411 | | 1979 | 21.927196804648 | | 1978 | 24.753506457437 | | 1977 | 24.613189948425 | | 1976 | 23.289533303126 | | 1975 | 25.202101859337 | | 1974 | 30.833333333333 | | 1973 | 32.436974789916 | | 1972 | 32.288586635127 |
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