| Year | Value | | 2021 | 46.728305455553 | | 2020 | 46.924914612757 | | 2019 | 47.109535678021 | | 2018 | 47.312138835041 | | 2017 | 47.532742545924 | | 2016 | 47.771328348565 | | 2015 | 48.026603895505 | | 2014 | 48.222078833195 | | 2013 | 48.417553770885 | | 2012 | 48.613028708576 | | 2011 | 48.808503646266 | | 2010 | 49.003978583956 | | 2009 | 49.190019385212 | | 2008 | 49.376060186467 | | 2007 | 49.562100987723 | | 2006 | 49.748141788978 | | 2005 | 49.934182590233 | | 2004 | 50.120223391489 | | 2003 | 50.306264192744 | | 2002 | 50.492304994 | | 2001 | 50.678345795255 | | 2000 | 50.864386596511 | | 1999 | 51.11393242869 | | 1998 | 51.36347826087 | | 1997 | 51.613024093049 | | 1996 | 51.862569925228 | | 1995 | 52.112115757408 | | 1994 | 52.361661589587 | | 1993 | 52.611207421767 | | 1992 | 52.860753253946 | | 1991 | 53.110299086126 | | 1990 | 53.359844918305 |
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