| Year | Value | | 2022 | 9.2655155155155 | | 2021 | 7.2260630741548 | | 2020 | 2.4151309408341 | | 2019 | 1.9517682105289 | | 2018 | 4.2699902046708 | | 2017 | 5.5911159096166 | | 2016 | 6.3976948026876 | | 2015 | 4.7844470069389 | | 2014 | 2.9169269206746 | | 2013 | 3.2542391099885 | | 2012 | 8.8914509106232 | | 2011 | 4.5242115050527 | | 2010 | 3.9110619553403 | | 2009 | 5.7370603614563 | | 2008 | 4.8585906281494 | | 2007 | 3.678995747417 | | 2006 | 2.3114991851442 | | 2005 | 1.3824465666212 | | 2004 | 3.9618003025719 | | 2003 | 4.268953958395 | | 2002 | 1.4183019234505 | | 2001 | 4.2259883485467 | | 2000 | 0.33916318907177 | | 1999 | 2.645511133928 | | 1998 | 4.9501616379311 | | 1997 | 5.7335227535719 | | 1996 | 18.679075860175 | | 1995 | 29.7796264865 | | 1994 | 29.047656117307 | | 1993 | 20.540326123583 | | 1992 | 31.669661911715 | | 1991 | 25.886386934851 | | 1990 | 16.652534388543 | | 1989 | 9.3043612584317 | | 1988 | 5.9115449637349 | | 1987 | 7.4412609128725 | | 1986 | 12.37160916513 | | 1985 | 10.482287044447 | | 1984 | 8.116397955171 | | 1983 | 5.9671639303272 | | 1982 | 6.5425096300767 | | 1981 | 14.654842636063 | | 1980 | 9.5178244975496 | | 1979 | 11.348600508609 | | 1978 | 17.523923445503 | | 1977 | 11.989283322105 | | 1976 | 9.4307354017456 | | 1975 | 8.2303166526514 | | 1974 | 4.6996124034169 | | 1973 | 6.1728395062271 | | 1972 | 3.6563071298324 | | 1971 | 2.6266416510563 | | 1970 | 6.5999999990002 |
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