| Year | Value | | 2021 | 39.887506978357 | | 2020 | 39.843214149907 | | 2019 | 39.797851757679 | | 2018 | 39.750997354766 | | 2017 | 39.705589694883 | | 2016 | 39.644690804143 | | 2015 | 39.595374339952 | | 2014 | 39.506969518184 | | 2013 | 39.432112669273 | | 2012 | 39.363562860238 | | 2011 | 39.282761340582 | | 2010 | 39.199560603772 | | 2009 | 39.091680543013 | | 2008 | 38.980198466071 | | 2007 | 38.854178360318 | | 2006 | 38.733127524983 | | 2005 | 38.606183045219 | | 2004 | 38.482844636723 | | 2003 | 38.359812175192 | | 2002 | 38.243898625269 | | 2001 | 38.112001988714 | | 2000 | 37.986456736805 | | 1999 | 37.954460342123 | | 1998 | 37.787225311692 | | 1997 | 37.619897842715 | | 1996 | 37.452101172114 | | 1995 | 37.286005872352 | | 1994 | 37.118778832265 | | 1993 | 36.952207162355 | | 1992 | 36.805530330493 | | 1991 | 36.223436275108 | | 1990 | 36.047777485548 |
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