| Year | Value | | 2021 | 32.208603320254 | | 2020 | 32.121535939466 | | 2019 | 32.034468558678 | | 2018 | 31.94740117789 | | 2017 | 31.860333797102 | | 2016 | 31.773266416314 | | 2015 | 31.685717850795 | | 2014 | 31.598223363018 | | 2013 | 31.510731528104 | | 2012 | 31.423241550649 | | 2011 | 31.335755816381 | | 2010 | 31.248271939332 | | 2009 | 31.150262753612 | | 2008 | 31.052257325186 | | 2007 | 30.954254863087 | | 2006 | 30.855765774304 | | 2005 | 30.757282791636 | | 2004 | 30.658806690322 | | 2003 | 30.560337462247 | | 2002 | 30.461875099298 | | 2001 | 30.363419593364 | | 2000 | 30.264970170593 | | 1999 | 30.156053920576 | | 1998 | 30.047144388611 | | 1997 | 29.938242331484 | | 1996 | 29.829347740238 | | 1995 | 29.72046060592 | | 1994 | 29.612551002932 | | 1993 | 29.504640963169 | | 1992 | 29.396730486627 | | 1991 | 29.288819573304 | | 1990 | 29.180908223198 |
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