| Year | Value | | 2022 | 14.608143949243 | | 2021 | 5.1109653438285 | | 2020 | 3.3267438576674 | | 2019 | 3.3385863538201 | | 2018 | 2.8502479259465 | | 2017 | 2.3482428115015 | | 2016 | 0.39476930668639 | | 2015 | 0.061644680064167 | | 2014 | 0.22756627098822 | | 2013 | 1.733199849831 | | 2012 | 5.6521451708865 | | 2011 | 3.9299209893507 | | 2010 | 4.8555579569196 | | 2009 | 4.2117117117117 | | 2008 | 6.0425125388106 | | 2007 | 7.9587451654491 | | 2006 | 3.93032603841 | | 2005 | 3.5615171137835 | | 2004 | 6.7443467956947 | | 2003 | 4.6610169491525 | | 2002 | 5.2654482158399 | | 2001 | 9.1168091168091 | | 2000 | 9.8036101690812 | | 1999 | 9.9977440930337 | | 1998 | 14.153789654534 | | 1997 | 18.30507441438 | | 1996 | 23.469030191918 | | 1995 | 28.305468370665 | | 1994 | 18.868074986928 | | 1993 | 22.464234613381 | | 1992 | 23.655720780655 | | 1991 | 34.81754290727 | | 1990 | 28.369599653278 | | 1989 | 17.149151997396 | | 1988 | 15.723549070356 | | 1987 | 8.6743141773324 | | 1986 | 5.2916617007109 | | 1985 | 6.9423450187915 | | 1984 | 8.4678548764602 | | 1983 | 7.2798957327949 | | 1982 | 6.8358050825954 | | 1981 | 4.6614139439475 | | 1980 | 9.2858574392134 | | 1979 | 8.976412347003 | | 1978 | 4.6871427485311 | | 1977 | 3.9088956956482 | | 1976 | 5.2283983330866 | | 1975 | 3.8421599179382 | | 1974 | 1.7970401682347 | | 1973 | 3.387978141767 |
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