| Year | Value | | 2022 | 30.60238916101 | | 2021 | 30.246675220588 | | 2020 | 29.994990437722 | | 2019 | 30.090542245851 | | 2018 | 29.869550546077 | | 2017 | 30.168717059358 | | 2016 | 29.895358131385 | | 2015 | 29.621093771067 | | 2014 | 29.452577598441 | | 2013 | 29.596211014643 | | 2012 | 29.444710087558 | | 2011 | 29.231023408191 | | 2010 | 28.774410578885 | | 2009 | 28.660774026926 | | 2008 | 28.612585258718 | | 2007 | 28.337916833033 | | 2006 | 28.173560388173 | | 2005 | 28.064212988151 | | 2004 | 27.998291757246 | | 2003 | 28.119031087148 | | 2002 | 28.265740136653 | | 2001 | 28.527255446816 | | 2000 | 28.775101312325 | | 1999 | 29.156644925973 | | 1998 | 29.673726866358 | | 1997 | 30.320084517494 | | 1996 | 30.056156134368 | | 1995 | 29.793252432544 | | 1994 | 29.772924101248 | | 1993 | 29.735332493119 | | 1992 | 29.642649268824 | | 1991 | 29.687133956915 |
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