| Year | Value | | 2022 | 8.3905763411863 | | 2021 | 3.0931351197642 | | 2020 | 0.32275301729974 | | 2019 | 0.69951899445874 | | 2018 | 1.6749813686379 | | 2017 | 1.9560763336396 | | 2016 | 0.20259800042645 | | 2015 | 0.50036570990324 | | 2014 | 0.15111483752724 | | 2013 | 1.4085810918302 | | 2012 | 2.4461278236681 | | 2011 | 3.1961018883379 | | 2010 | 1.7998645772877 | | 2009 | 0.28781308353524 | | 2008 | 4.0753433595734 | | 2007 | 2.7867974580495 | | 2006 | 3.5155757683213 | | 2005 | 3.3688140975038 | | 2004 | 3.0392488109093 | | 2003 | 3.0388883939666 | | 2002 | 3.0656568590222 | | 2001 | 3.5898341333811 | | 2000 | 3.4335156341877 | | 1999 | 2.3103481398707 | | 1998 | 1.8343299990841 | | 1997 | 1.9710739558293 | | 1996 | 3.5588455933856 | | 1995 | 4.673803376247 | | 1994 | 4.7184137396733 | | 1993 | 4.5690717368181 | | 1992 | 5.9245312622849 | | 1991 | 5.9342134433592 | | 1990 | 6.7218195222866 | | 1989 | 6.791435840251 | | 1988 | 4.8372706649036 | | 1987 | 5.2480186348959 | | 1986 | 8.7949393229032 | | 1985 | 8.8144550667839 | | 1984 | 11.280276560404 | | 1983 | 12.17407273517 | | 1982 | 14.415002054833 | | 1981 | 14.549345717032 | | 1980 | 15.561902095725 | | 1979 | 15.660235597177 | | 1978 | 19.773670497366 | | 1977 | 24.538063292921 | | 1976 | 17.624880052748 | | 1975 | 16.953285933498 | | 1974 | 15.680373398539 | | 1973 | 11.416707613708 | | 1972 | 8.2722875494194 | | 1971 | 8.236887148936 | | 1970 | 5.7311448429353 | | 1969 | 2.1603471359987 | | 1968 | 4.9543661173646 | | 1967 | 6.3916310878212 | | 1966 | 6.2403670829799 | | 1965 | 13.21413783822 | | 1964 | 6.9792467398961 | | 1963 | 8.7436976840915 | | 1962 | 5.7064771927131 | | 1961 | 0.80925287388217 | | 1960 | 1.1777710840963 |
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