| Year | Value | | 2022 | 30.121571670496 | | 2021 | 30.426134053427 | | 2020 | 21.928161804691 | | 2019 | 15.361950613917 | | 2018 | 15.676238113924 | | 2017 | 18.683428332397 | | 2016 | 19.912907200701 | | 2015 | 18.892357537489 | | 2014 | 11.409748316487 | | 2013 | 5.5877546765372 | | 2012 | 15.721865931081 | | 2011 | 6.2866367271504 | | 2010 | 0.3532099913808 | | 2009 | 5.3078486389779 | | 2008 | 0.3212820144373 | | 2007 | 9.2517595468251 | | 2006 | 11.746923496707 | | 2005 | 3.5817991915522 | | 2004 | 6.0499692438732 | | 2003 | 9.7933719009995 | | 1997 | 7.5389101360695 | | 1996 | -3.3115796584465 | | 1995 | 9.4531000577547 | | 1994 | -2.339214571854 | | 1993 | 0.15817787240445 | | 1992 | 11.703743206586 | | 1991 | 8.7510551057194 | | 1990 | 21.853656919655 | | 1989 | 17.457103696587 | | 1988 | 30.114742580492 | | 1987 | 42.297488146995 | | 1986 | 29.350054362052 | | 1985 | 22.88075578133 | | 1984 | 12.137083046866 | | 1983 | 10.041405853702 | | 1982 | 19.867909347286 | | 1981 | 24.289695157835 | | 1980 | 16.354909875119 | | 1979 | 11.382899580864 | | 1978 | 3.8055235248873 |
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