| Year | Value | | 2019 | 4.1002896451846 | | 2018 | 3.673814104068 | | 2017 | 4.66018463956 | | 2016 | 1.281928130619 | | 2015 | -1.1127899251097 | | 2014 | 1.7695032208973 | | 2013 | 1.8141043604911 | | 2012 | 4.5333475388877 | | 2011 | 9.4322024017722 | | 2010 | 5.8242185331187 | | 2009 | 3.6438618925833 | | 2008 | 8.1081081081078 | | 2007 | 4.0342298288507 | | 2006 | 7.3076626282894 | | 2005 | 6.0821872953504 | | 2004 | 1.3944223107569 | | 2003 | 1.6194331983806 | | 2002 | 0.12524945805599 | | 2001 | 2.5778349043129 | | 2000 | 2.4358130348914 | | 1999 | 1.5600624024961 | | 1998 | -1.2688866070121 | | 1997 | 7.7105387896988 | | 1996 | 2.3861522284233 | | 1995 | 1.8788627935723 | | 1994 | 0.077204388460249 | | 1993 | 1.1134393360449 | | 1992 | 6.0938930299464 | | 1991 | 6.2575266327002 | | 1990 | 3.0745727107802 | | 1989 | 6.1901140684412 | | 1988 | 4.8588591781405 | | 1987 | 3.3117311074325 | | 1986 | 1.3300684516192 | | 1985 | 3.9151052508279 | | 1984 | 4.685797311856 | | 1983 | 5.2302987828884 | | 1982 | 10.332466437056 | | 1981 | 14.567563214689 | | 1980 | 14.430519720394 | | 1979 | 13.16983554318 | | 1978 | 9.4823825910176 | | 1977 | 8.35236969935 | | 1976 | 4.9867681111319 | | 1975 | 20.294468762529 | | 1974 | 38.922928087811 | | 1973 | 16.855081826021 | | 1972 | 11.876656227533 | | 1971 | 7.4692556635386 | | 1970 | 7.2842163736852 | | 1969 | 5.8352318660549 | | 1968 | 7.4887431868762 | | 1967 | 3.6348751533576 |
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