| Year | Value | | 2021 | 35.980103168755 | | 2020 | 35.860353721444 | | 2019 | 35.740604274134 | | 2018 | 35.620854826824 | | 2017 | 35.501105379514 | | 2016 | 35.381355932203 | | 2015 | 35.307663964628 | | 2014 | 35.130803242447 | | 2013 | 34.953942520265 | | 2012 | 34.777081798084 | | 2011 | 34.600221075903 | | 2010 | 34.423360353721 | | 2009 | 34.089904200442 | | 2008 | 33.740907835374 | | 2007 | 33.407605192892 | | 2006 | 33.068213200773 | | 2005 | 32.731958762887 | | 2004 | 32.363001103347 | | 2003 | 32.027213386044 | | 2002 | 31.685661764706 | | 2001 | 30.834312573443 | | 2000 | 30.507095724487 | | 1999 | 30.463707855012 | | 1998 | 30.420319985537 | | 1997 | 30.376932116062 | | 1996 | 30.333544246588 | | 1995 | 30.290156377113 | | 1994 | 30.246768507638 | | 1993 | 30.203380638163 | | 1992 | 30.159992768688 | | 1991 | 30.116604899214 | | 1990 | 30.073217029739 |
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