| Year | Value | | 2022 | 4.2312479827462 | | 2021 | 1.0869074651941 | | 2020 | 1.3527611067533 | | 2019 | 2.4645675615119 | | 2018 | 4.7490665208323 | | 2017 | 2.6519258314389 | | 2016 | 2.1067071278405 | | 2015 | 0.3387951887535 | | 2014 | 4.6904575182629 | | 2013 | 0.50544105891561 | | 2012 | 2.6524182869563 | | 2011 | 1.2633170783742 | | 2010 | 1.4615440272047 | | 2009 | 1.8857075457792 | | 2008 | 5.2643014557529 | | 2007 | 5.0303188367995 | | 2006 | -1.4094013660098 | | 2005 | 3.708333333333 | | 2004 | 0.40820530743925 | | 2003 | 2.2353531355154 | | 2002 | 0.036682889397139 | | 2001 | 2.1376205270147 | | 2000 | 0.50492002583486 | | 1999 | -1.9366039760363 | | 1998 | 1.448738542946 | | 1997 | 3.973450075453 | | 1996 | 0.68969337728164 | | 1995 | 9.6465310407962 | | 1994 | 36.116245696298 | | 1993 | 0.53374655647419 | | 1992 | -9.5429133033658 | | 1991 | -11.686112692089 | | 1990 | 7.7253218884121 | | 1989 | 6.740837696335 | | 1988 | -8.7761194029851 | | 1987 | 0.94618568894144 | | 1986 | 6.2853551225645 | | 1985 | 7.3549257759783 | | 1984 | 5.857142857143 | | 1983 | 10.671936758893 | | 1982 | 16.685796879749 | | 1981 | 8.70650214893 | | 1980 | 12.34035925656 | | 1979 | 7.9526985375144 | | 1978 | 10.764169097681 | | 1977 | 13.852569086284 | | 1976 | 20.171564463972 | | 1975 | 28.452942637234 | | 1974 | 12.072804185662 | | 1973 | 6.2071411681434 | | 1972 | 3.4870916434787 | | 1971 | 3.8632608970158 | | 1970 | 3.8126649076679 | | 1969 | 2.9751392473965 | | 1968 | 2.3356040592984 | | 1967 | 1.9777415468267 | | 1966 | 3.6441113809677 | | 1965 | 2.4384736959592 | | 1964 | 3.3284081190083 | | 1963 | 7.1583333325 |
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