| Year | Value | | 2022 | 6.9638714794047 | | 2021 | 9.2997889727063 | | 2020 | 10.521874551266 | | 2019 | 8.1481519871063 | | 2018 | 7.9707653481035 | | 2017 | 7.9577755247133 | | 2016 | 7.6116538109354 | | 2015 | 6.5309945186998 | | 2014 | 6.0099060186975 | | 2013 | 6.1947827725511 | | 2012 | 6.41459569286 | | 2011 | 6.5970185794309 | | 2009 | 7.7805278058491 | | 2008 | 6.7565668221198 | | 2007 | 7.365420040882 | | 2006 | 7.2417500626591 | | 2005 | 8.3298742259161 | | 2004 | 8.4522092868203 | | 2003 | 9.4032459577605 | | 2002 | 9.8580423598622 | | 2001 | 9.0661434187223 | | 1999 | 9.7364180848446 | | 1998 | 8.9842181667144 | | 1997 | 8.575310592531 | | 1996 | 8.8929168893482 | | 1995 | 8.4438799396676 | | 1993 | 6.1099654652029 | | 1992 | 6.6350635850667 |
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