| Year | Value | | 2022 | 4.7235934718387 | | 2021 | 4.7343808554313 | | 2020 | 4.1118181088694 | | 2019 | 3.9559873939708 | | 2018 | 3.9972412177528 | | 2017 | 3.7226152767624 | | 2016 | 4.1739714696302 | | 2015 | 3.6817220183037 | | 2014 | 3.7962024988346 | | 2013 | 3.8275320606864 | | 2012 | 4.4420108748494 | | 2011 | 5.3838931795535 | | 2010 | 6.8525384943469 | | 2009 | 6.7381211796545 | | 2008 | 7.2159149360693 | | 2007 | 8.6663199024039 | | 2006 | 9.5314718087189 | | 2005 | 10.705595974713 | | 2004 | 13.246447040136 | | 2003 | 13.428943929464 | | 2002 | 16.155894870027 | | 1999 | 20.08185606154 | | 1998 | 20.061596039141 | | 1997 | 19.673920552677 | | 1995 | 19.354891446508 | | 1994 | 21.076058982535 | | 1993 | 20.937216871917 | | 1992 | 20.63930013459 | | 1991 | 21.918284555201 | | 1990 | 21.229471146602 |
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