| Year | Value | | 2022 | 5.4248936157288 | | 2021 | 6.7196962296037 | | 2020 | 4.6502735170111 | | 2019 | 5.1130071095337 | | 2018 | -1.1728634757331 | | 2017 | 7.807688948772 | | 2016 | 8.2309764752456 | | 2015 | 7.3853523207202 | | 2014 | 7.8761620217542 | | 2013 | 8.5692561019055 | | 2012 | 9.0196914583098 | | 2011 | 28.151346926551 | | 2010 | 27.34787941258 | | 2009 | 23.485174478808 | | 2008 | 33.740082842685 | | 2007 | 37.889175564551 | | 2006 | 32.406231591003 | | 2005 | 35.270258942981 | | 2004 | 36.955558701997 | | 2003 | 31.89931038761 | | 2002 | 31.297647424682 | | 2001 | 28.634581827275 | | 2000 | 18.035602646112 | | 1999 | 6.6145303242698 | | 1998 | 8.4941199407971 | | 1997 | 7.106962538422 | | 1996 | 0.72686339589659 | | 1995 | 3.1372260259496 | | 1994 | 5.7788757475612 | | 1993 | 3.0692505063191 | | 1992 | 3.8174086491236 | | 1991 | 0.86991521258695 | | 1990 | 2.061558075245 | | 1989 | 6.6858992866671 | | 1988 | 9.0748571737803 | | 1987 | 9.1722562474733 | | 1986 | 10.992015029032 | | 1985 | 4.5377323428666 | | 1984 | 0.53968885060265 | | 1983 | 4.9609786709124 | | 1982 | 3.9424497027211 | | 1981 | 4.6263559911997 | | 1980 | 4.0906898663604 | | 1979 | 5.1889451321167 | | 1978 | 6.7840711871775 | | 1977 | 8.3854121114192 |
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