| Year | Value | | 2021 | 4.8641947769829 | | 2020 | 0.22641194914324 | | 2019 | 4.9514032455038 | | 2018 | 4.5905311896066 | | 2017 | 4.7598254086739 | | 2016 | 2.70243575648 | | 2015 | 1.764969581312 | | 2014 | 4.9382548166218 | | 2013 | 8.6327598668961 | | 2012 | 6.2381523407879 | | 2011 | 9.5978865330849 | | 2010 | 0.89491189173751 | | 2009 | 10.6381837401 | | 2008 | 1.8310154224325 | | 2007 | 0.81101137590143 | | 2006 | 2.8358035169709 | | 2005 | 3.2218628152477 | | 2004 | 2.2987741476784 | | 2003 | 1.7291693208356 | | 2002 | 1.8914984722969 | | 2001 | 2.5844616496366 | | 2000 | 11.351044349451 | | 1999 | 2.7209095719432 | | 1998 | 1.0298176251924 | | 1997 | 3.945415124335 | | 1996 | -1.4834106171785 | | 1995 | 1.895152559618 | | 1994 | -5.9921702558855 | | 1993 | 2.6213735466216 | | 1992 | 9.3521975269229 | | 1991 | -5.2750937502537 | | 1990 | 4.3002354060764 | | 1989 | -2.1122272481434 | | 1988 | 2.3274039493447 | | 1987 | 2.2850279798825 | | 1986 | 1.9215193987532 | | 1985 | 1.2039125195854 | | 1984 | 4.4482845486121 | | 1983 | 4.7430930407875 | | 1982 | 5.9183831603119 | | 1981 | 3.7374673175834 |
|