| Year | Value | | 2022 | 1.8813670719691 | | 2021 | 1.5687583444588 | | 2020 | 0.25096202108087 | | 2019 | 2.8832085377399 | | 2018 | 2.4061343204654 | | 2017 | 1.4938724393953 | | 2016 | 2.4093074386222 | | 2015 | 2.9908481932258 | | 2014 | 4.4236453201971 | | 2013 | 4.3379934210526 | | 2012 | 4.0539095090384 | | 2011 | 5.3052489299392 | | 2010 | 2.2928908860467 | | 2009 | 0.57944141847264 | | 2008 | 4.3031548410491 | | 2007 | 2.0350271336951 | | 2006 | 2.0002516039753 | | 2005 | 0.82644628099184 | | 2004 | 0.27472527472526 | | 2003 | -2.6737967914439 | | 2002 | -2.9831387808042 | | 2001 | -1.6581632653061 | | 2000 | -3.6855036855037 | | 1999 | -4.0094339622644 | | 1998 | 2.9126213592239 | | 1997 | 5.7766367137352 | | 1996 | 6.2755798090041 | | 1995 | 9.0773809523809 | | 1994 | 8.7378640776698 | | 1993 | 8.8028169014086 | | 1992 | 9.6525096525096 | | 1991 | 11.158798283262 | | 1990 | 10.42654028436 | | 1989 | 10.182767624021 | | 1988 | 7.8873239436618 | | 1987 | 5.654761904762 | | 1986 | 3.3846153846153 | | 1985 | 3.5031847133757 | | 1984 | 8.6505190311418 | | 1983 | 9.8859315589355 | | 1982 | 10.970464135021 |
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