| Year | Value | | 2022 | 26.780609971385 | | 2021 | 23.464402547837 | | 2020 | 21.469509343524 | | 2019 | 22.289447925479 | | 2018 | 23.115947990323 | | 2017 | 20.357607955295 | | 2016 | 20.014492094991 | | 2015 | 20.244509012793 | | 2014 | 21.482869936478 | | 2013 | 19.855688523715 | | 2012 | 21.296326228337 | | 2011 | 22.054821757328 | | 2010 | 23.704158178287 | | 2009 | 22.44389205269 | | 2008 | 24.803855039534 | | 2007 | 22.449786798896 | | 2006 | 23.044843951515 | | 2005 | 20.086735923128 | | 2004 | 20.241971472489 | | 2003 | 19.275072674419 | | 2002 | 18.960697674877 | | 2001 | 20.254936559612 | | 2000 | 20.654017061315 | | 1999 | 20.037017647086 | | 1998 | 18.244775976091 | | 1997 | 23.000497373625 | | 1996 | 28.422860932769 | | 1995 | 31.431773461678 | | 1994 | 28.20921103555 | | 1993 | 33.372290046487 | | 1992 | 32.505689849309 | | 1991 | 33.00233164175 | | 1990 | 28.401450230718 |
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