| Year | Value | | 2022 | 4.2291556889712 | | 2021 | 1.3460937724312 | | 2020 | 0.33329435062838 | | 2019 | 0.7615140472656 | | 2018 | 4.4623110847548 | | 2017 | 3.323894475761 | | 2016 | 0.77843046305414 | | 2015 | 0.87685135970405 | | 2014 | 2.8994790500606 | | 2013 | 4.8246231426954 | | 2012 | 4.5152295667099 | | 2011 | 4.1624416292779 | | 2010 | 4.8455187585212 | | 2009 | 0.73906974314478 | | 2008 | 13.971231001273 | | 2007 | 4.7439063902165 | | 2006 | 6.2517246665644 | | 2005 | 3.4936853461953 | | 2004 | 3.361868214766 | | 2003 | 1.63 | | 2002 | 1.8329938900205 | | 2001 | 1.7722043735102 | | 2000 | 0.66688092559796 | | 1999 | 0.60625656777943 | | 1998 | 3.091666666667 | | 1997 | 3.0378842030025 | | 1996 | 6.5012180267959 | | 1995 | 2.3531245130127 | | 1994 | 3.5166962413289 | | 1993 | 3.3166666666671 | | 1992 | 3.9958356055719 | | 1991 | 8.1554959785521 | | 1990 | 16.192137561523 | | 1989 | 25.712719298245 | | 1988 | 6.6132264529058 | | 1987 | 0.19999999999991 | | 1985 | 2.9850746271476 | | 1984 | 3.8474727383761 | | 1983 | 5.0201670983146 | | 1982 | 7.4280408542249 | | 1981 | 7.6999999999997 | | 1980 | 11.111111111111 | | 1979 | 14.246491763078 | | 1978 | 6.9215212995241 | | 1977 | 14.566517189388 | | 1976 | 11.5 | | 1975 | 11.979823455309 | | 1974 | 19.42771084352 | | 1973 | 11.129707112134 | | 1972 | 7.6576576576576 | | 1971 | 4.8158640236527 | | 1970 | 5.8999999989999 |
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