| Year | Value | | 2021 | 11.214646571961 | | 2020 | 10.884671205402 | | 2019 | 11.936348829935 | | 2018 | 12.022665859469 | | 2017 | 12.94596624118 | | 2016 | 13.550725172419 | | 2015 | 14.056862129339 | | 2014 | 14.840790714027 | | 2013 | 15.310235280489 | | 2012 | 15.613146742555 | | 2011 | 14.794353171378 | | 2010 | 13.332195310377 | | 2009 | 14.940501532664 | | 2008 | 14.662958256786 | | 2007 | 14.303722837197 | | 2006 | 14.516196982493 | | 2005 | 14.826391060712 | | 2004 | 15.199093762657 | | 2003 | 15.495655122514 | | 2002 | 17.446955087641 | | 2001 | 17.794888805062 | | 2000 | 13.666908903174 | | 1999 | 14.093708023567 | | 1998 | 16.730157497273 | | 1997 | 19.753366809205 | | 1996 | 19.377926315955 |
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