| Year | Value | | 2022 | 7.8073754099672 | | 2021 | 2.3581429624171 | | 2020 | 0.33458462542853 | | 2019 | 0.93904448105439 | | 2018 | 0.48837016803244 | | 2017 | 0.3405315614619 | | 2016 | 0.0083063377356599 | | 2015 | 0.28987907901277 | | 2014 | 0.1825423166279 | | 2013 | 0.50871486948547 | | 2012 | 1.6962089729455 | | 2011 | 2.5571888318692 | | 2010 | 0.92209582902454 | | 2009 | -4.4781033915048 | | 2008 | 4.0603049511737 | | 2007 | 4.8971156438134 | | 2006 | 3.9316398954053 | | 2005 | 2.4296919839296 | | 2004 | 2.1996285071855 | | 2003 | 3.4904896802914 | | 2002 | 4.614733276884 | | 2001 | 4.8729048729048 | | 2000 | 5.5907172995781 | | 1999 | 1.6319237641453 | | 1998 | 2.4155178723923 | | 1997 | 1.5256052171453 | | 1996 | 1.7537321389601 | | 1995 | 2.524867280053 | | 1994 | 2.3091987506149 | | 1993 | 1.4694208843173 | | 1992 | 3.0699974346696 | | 1991 | 3.2108170275135 | | 1990 | 3.3173212989425 | | 1989 | 4.0890427302037 | | 1988 | 2.134571568596 | | 1987 | 3.1594076405343 | | 1986 | 3.8270393152441 | | 1985 | 5.3954973146638 | | 1984 | 8.6511138376541 | | 1983 | 10.447629524083 | | 1982 | 17.147114203212 | | 1981 | 20.373522894777 | | 1980 | 18.154443303819 | | 1979 | 13.295453985261 | | 1978 | 7.711141180048 | | 1977 | 13.472225263393 | | 1976 | 17.985695861338 | | 1975 | 20.875850340195 | | 1974 | 16.976127321205 | | 1973 | 11.41485038733 | | 1972 | 8.6058174530107 | | 1971 | 8.9617486341767 | | 1970 | 8.2071901609103 | | 1969 | 7.4186991859755 | | 1968 | 4.6808510638299 | | 1967 | 3.1833150395518 | | 1966 | 3.0542986414027 | | 1965 | 4.9881235154395 | | 1964 | 6.7172897192629 | | 1963 | 2.4536205866893 | | 1962 | 4.2637271214908 | | 1961 | 2.7569993586355 | | 1960 | 0.45083726943178 |
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