| Year | Value | | 2022 | 6.872574385511 | | 2021 | 3.0666666666667 | | 2020 | 0.14487792581398 | | 2019 | 1.4456597688825 | | 2018 | 1.7321687976694 | | 2017 | 1.5094948510963 | | 2016 | 0.49174700844517 | | 2015 | 0.51442613712546 | | 2014 | 0.90679400043425 | | 2013 | 1.5047233025188 | | 2012 | 2.0084888478296 | | 2011 | 2.0751728373587 | | 2010 | 1.1038103778926 | | 2009 | 0.31273900736845 | | 2008 | 2.6283798163722 | | 2007 | 2.2983440070095 | | 2006 | 1.5774264284056 | | 2005 | 1.5469111475133 | | 2004 | 1.6657369665599 | | 2003 | 1.0342221862856 | | 2002 | 1.4208061555153 | | 2001 | 1.9838573133447 | | 2000 | 1.4402683871974 | | 1999 | 0.58543306423078 | | 1998 | 0.9111835350144 | | 1997 | 1.9393719892273 | | 1996 | 1.4497270196324 | | 1995 | 1.7061604131708 | | 1994 | 2.6930563985495 | | 1993 | 4.4745765075281 | | 1992 | 5.0569779673173 | | 1991 | 4.0470325975347 | | 1990 | 2.6964682429239 | | 1989 | 2.7805695556975 | | 1988 | 1.2741189400692 | | 1987 | 0.24990610870503 | | 1986 | 0.12941336085474 | | 1985 | 2.0662330121658 | | 1984 | 2.4057933993196 | | 1983 | 3.2934147430285 | | 1982 | 5.2410450722842 | | 1981 | 6.3442427774632 | | 1980 | 5.4410575446035 | | 1979 | 4.043620064734 | | 1978 | 2.7186969612334 | | 1977 | 3.7341624063515 | | 1976 | 4.2466310229921 | | 1975 | 5.9103362632411 | | 1974 | 6.986431093275 | | 1973 | 7.032023993039 | | 1972 | 5.4849331221432 | | 1971 | 5.2409744827309 | | 1970 | 3.4502493636089 | | 1969 | 1.912678487976 | | 1968 | 1.470289313277 | | 1967 | 1.7960499221318 | | 1966 | 3.5330603547769 | | 1965 | 3.2423192366813 | | 1964 | 2.3357358117783 | | 1963 | 2.9669597758771 | | 1962 | 2.8432701979906 | | 1961 | 2.2936950070088 | | 1960 | 1.536612342952 |
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