| Year | Value | | 2021 | 50.062650990498 | | 2020 | 50.321428571429 | | 2019 | 50.58020615236 | | 2018 | 50.83898373329 | | 2017 | 51.097761314221 | | 2016 | 51.356538895152 | | 2015 | 51.615316476083 | | 2014 | 51.78362860364 | | 2013 | 51.951940731197 | | 2012 | 52.120252858753 | | 2011 | 52.28856498631 | | 2010 | 52.456877113867 | | 2009 | 52.739656144307 | | 2008 | 53.022435174746 | | 2007 | 53.305214205186 | | 2006 | 53.587993235626 | | 2005 | 53.870772266065 | | 2004 | 54.153551296505 | | 2003 | 54.436330326945 | | 2002 | 54.719109357384 | | 2001 | 55.001888387824 | | 2000 | 55.284667418264 | | 1999 | 55.647733129328 | | 1998 | 56.010798840393 | | 1997 | 50.574385926889 | | 1996 | 50.900101141453 | | 1995 | 51.225816356018 | | 1994 | 51.551531570582 | | 1993 | 51.877246785147 | | 1992 | 52.202961999711 | | 1991 | 52.528677214275 | | 1990 | 52.85439242884 |
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