| Year | Value | | 2022 | 4.3171066723052 | | 2021 | 4.4707815629828 | | 2020 | 4.982543723675 | | 2019 | 4.7877058407856 | | 2018 | 4.119886152569 | | 2017 | 3.8497305765468 | | 2016 | 4.0903492169932 | | 2015 | 4.2392257857323 | | 2014 | 3.9433782647458 | | 2013 | 3.9972445573048 | | 2012 | 3.5837669187374 | | 2011 | 3.8539464411557 | | 2010 | 4.2656460559377 | | 2009 | 4.1570499078351 | | 2008 | 3.3955793627066 | | 2007 | 3.0425747012797 | | 2006 | 2.9476131562586 | | 2005 | 2.8719313629181 | | 2004 | 2.7419967049371 | | 2003 | 2.7283722137797 | | 2002 | 2.6977147488641 | | 2001 | 3.1272493853097 | | 2000 | 3.560024872537 | | 1999 | 3.6973742308425 | | 1998 | 3.528096003182 | | 1997 | 3.9093985598059 | | 1996 | 3.2818670042301 | | 1995 | 4.0593119083361 | | 1993 | 2.2966443331905 | | 1992 | 2.2033898305085 |
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