| Year | Value | | 2020 | 5.5339316325502 | | 2019 | 5.9092462826867 | | 2018 | 6.4601477235145 | | 2017 | 7.0061934473787 | | 2016 | 7.3100789770591 | | 2015 | 8.124801640585 | | 2014 | 8.1071039334192 | | 2013 | 8.5423283320556 | | 2012 | 8.1458494957331 | | 2011 | 8.9543465482333 | | 2010 | 9.2166515958337 | | 2009 | 9.3857425605056 | | 2008 | 10.311446285486 | | 2007 | 10.42000534188 | | 2006 | 12.041215718738 | | 2005 | 13.99137298091 | | 2004 | 15.712136128272 | | 2003 | 15.904534823679 | | 2002 | 18.507198787573 | | 2001 | 20.35633469889 | | 2000 | 24.390158295602 | | 1999 | 27.791051052199 | | 1998 | 30.061277282161 | | 1997 | 28.566321058277 | | 1996 | 31.56733720701 | | 1995 | 32.643007118349 | | 1994 | 37.213280371042 | | 1993 | 41.565842431105 | | 1992 | 46.936905436526 | | 1991 | 39.579252674401 | | 1990 | 34.74194456736 |
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