| Year | Value | | 2021 | 4.5330844490216 | | 2020 | 4.523236354274 | | 2019 | 4.5133882595263 | | 2018 | 4.5035401647786 | | 2017 | 4.4936920700309 | | 2016 | 4.4838439752832 | | 2015 | 4.4739958805355 | | 2014 | 4.4641477857879 | | 2013 | 4.4542996910402 | | 2012 | 4.4444515962925 | | 2011 | 4.4346035015448 | | 2010 | 4.4247554067971 | | 2009 | 4.4121524201854 | | 2008 | 4.3995494335736 | | 2007 | 4.3869464469619 | | 2006 | 4.3743434603501 | | 2005 | 4.3617404737384 | | 2004 | 4.3491374871267 | | 2003 | 4.3365345005149 | | 2002 | 4.3239315139032 | | 2001 | 4.3113285272915 | | 2000 | 4.2987255406797 | | 1999 | 4.2833592945417 | | 1998 | 4.2679930484037 | | 1997 | 4.2526268022657 | | 1996 | 4.2372605561277 | | 1995 | 4.2218943099897 | | 1994 | 4.2065274201854 | | 1993 | 4.1911611740474 | | 1992 | 4.1757949279094 | | 1991 | 4.1604286817714 | | 1990 | 4.1450624356334 |
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