| Year | Value | | 2022 | 14.621502447858 | | 2021 | 14.130003931499 | | 2020 | 13.950985707377 | | 2019 | 14.488473021251 | | 2018 | 14.04753327919 | | 2017 | 13.593793749214 | | 2016 | 13.087100691495 | | 2015 | 13.019610591534 | | 2014 | 13.015517179454 | | 2013 | 12.743822063173 | | 2012 | 12.305927114704 | | 2011 | 11.849000782321 | | 2010 | 11.63527559371 | | 2009 | 11.69893556733 | | 2008 | 13.033513690517 | | 2007 | 12.960409301734 | | 2006 | 13.127301440187 | | 2005 | 11.924224062403 | | 2004 | 11.364404389378 | | 2003 | 11.666432594908 | | 2002 | 11.66813069103 | | 2001 | 12.265508647 | | 2000 | 12.440324774509 | | 1999 | 12.89543708605 | | 1998 | 13.675463756703 | | 1997 | 14.861494931242 | | 1996 | 14.826641655221 | | 1995 | 14.266255235101 | | 1994 | 14.037888721076 | | 1993 | 13.680881180335 | | 1992 | 13.538873059324 | | 1991 | 12.809588353401 | | 1990 | 12.35461035892 |
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