| Year | Value | | 2022 | 25.428671177507 | | 2021 | 25.776588965615 | | 2020 | 23.695550319765 | | 2019 | 22.341726694538 | | 2018 | 21.70458900544 | | 2017 | 21.796346002112 | | 2016 | 20.705244881029 | | 2015 | 22.651987163429 | | 2014 | 23.579555848176 | | 2013 | 23.893559871141 | | 2012 | 24.288352752714 | | 2011 | 23.239969897215 | | 2010 | 21.78420057935 | | 2009 | 23.996967996185 | | 2008 | 21.893339705952 | | 2007 | 21.360623464154 | | 2006 | 21.657080478851 | | 2005 | 20.980011997237 | | 2004 | 21.521083947643 | | 2003 | 21.082940551503 | | 2002 | 21.779979953356 | | 2001 | 20.747578198498 | | 2000 | 21.195907959464 | | 1999 | 20.630597348838 | | 1998 | 21.628200705438 | | 1997 | 21.814165832526 | | 1996 | 20.90008760332 | | 1995 | 20.636648721364 | | 1994 | 21.87793934448 | | 1993 | 20.331848009138 | | 1992 | 18.342148684487 | | 1991 | 20.83633914004 | | 1990 | 24.447637527663 | | 1989 | 25.692972696228 |
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