| Year | Value | | 2022 | 5.5548266762702 | | 2021 | 6.8228707521193 | | 2020 | 7.1131732378936 | | 2019 | 6.9128975239635 | | 2018 | 6.8562390689357 | | 2017 | 7.0838671683977 | | 2016 | 7.4411804265034 | | 2015 | 7.4986883177387 | | 2014 | 7.5103929959474 | | 2013 | 7.5678628217492 | | 2012 | 7.5153348406415 | | 2011 | 8.0243732081331 | | 2010 | 8.7399301890125 | | 2009 | 9.148930746667 | | 2008 | 7.3420502668206 | | 2007 | 7.4715818274243 | | 2006 | 8.1868403662949 | | 2005 | 8.5692263237523 | | 2004 | 9.2161646123592 | | 2003 | 9.4809736047897 | | 2002 | 9.9492549702029 | | 2001 | 10.117328558526 | | 2000 | 10.16094770408 | | 1999 | 11.573974583658 | | 1998 | 10.768251535992 | | 1997 | 9.889676639162 | | 1996 | 9.0535484814094 | | 1995 | 8.5139282657723 | | 1994 | 8.3939186048469 | | 1993 | 7.0113443346314 | | 1992 | 6.5336187898693 |
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