| Year | Value | | 2021 | 49.903330288182 | | 2020 | 50.079644547795 | | 2019 | 50.255958807408 | | 2018 | 50.432273067021 | | 2017 | 50.608587326634 | | 2016 | 50.784901586247 | | 2015 | 50.96121584586 | | 2014 | 51.137530105473 | | 2013 | 51.313844365086 | | 2012 | 51.490158624699 | | 2011 | 51.666472884312 | | 2010 | 51.842787143925 | | 2009 | 52.019101403538 | | 2008 | 52.195415663151 | | 2007 | 52.371729922764 | | 2006 | 52.548044182377 | | 2005 | 52.72435844199 | | 2004 | 52.900672701603 | | 2003 | 53.076986961216 | | 2002 | 53.253301220829 | | 2001 | 53.429615480442 | | 2000 | 53.605929740055 | | 1999 | 53.985748691969 | | 1998 | 54.365567643883 | | 1997 | 54.745386595798 | | 1996 | 55.125205547712 | | 1995 | 55.505024499626 | | 1994 | 55.884843451541 | | 1993 | 56.264662403455 | | 1992 | 56.644481355369 | | 1991 | 57.024300307283 | | 1990 | 57.404119259198 |
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