| Year | Value | | 2023 | 28.507139274769 | | 2022 | 28.46003285653 | | 2021 | 28.7909549191 | | 2020 | 28.846376464596 | | 2019 | 29.080129015464 | | 2018 | 28.220997471898 | | 2017 | 27.341792906914 | | 2016 | 25.933947437361 | | 2015 | 25.037496907319 | | 2014 | 24.083468254696 | | 2013 | 24.448264641491 | | 2012 | 24.587427119778 | | 2011 | 24.973235690262 | | 2010 | 24.852141090583 | | 2009 | 25.059741035113 | | 2008 | 26.283362651905 | | 2007 | 26.77823706539 | | 2006 | 27.639635980056 | | 2005 | 26.539086644829 | | 2004 | 26.635735409567 | | 2003 | 27.378187759273 | | 2002 | 28.655107198637 | | 2001 | 29.067805105692 | | 2000 | 28.803706368819 | | 1999 | 28.974721560713 | | 1998 | 28.926749076624 | | 1997 | 29.011638446388 | | 1996 | 29.152225551925 | | 1995 | 29.069462311912 | | 1994 | 29.081313338312 | | 1993 | 29.089624872054 | | 1992 | 29.118675271196 | | 1991 | 29.245080555308 |
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