| Year | Value | | 2022 | 16.734002101199 | | 2021 | 13.981215925258 | | 2020 | 19.050099101962 | | 2019 | 16.837035845835 | | 2018 | 14.507128406145 | | 2017 | 15.023994698739 | | 2016 | 14.290534287027 | | 2015 | 12.880637614303 | | 2014 | 11.455953542206 | | 2013 | 11.862064636525 | | 2012 | 12.039369467557 | | 2011 | 13.011020862226 | | 2010 | 10.762314932704 | | 2009 | 11.252068731992 | | 2008 | 12.121366140984 | | 2007 | 11.358865886758 | | 2006 | 11.248331653102 | | 2005 | 10.001707976658 | | 2004 | 9.4283341560569 | | 2003 | 9.2885190567401 | | 2002 | 8.9990947128528 | | 2001 | 9.8595426932265 | | 2000 | 10.678687594952 | | 1999 | 10.323678042445 | | 1998 | 9.9725019829597 | | 1997 | 10.395239689468 | | 1996 | 17.049044056525 | | 1995 | 17.3461650627 | | 1994 | 16.716784289659 | | 1993 | 15.394566623545 | | 1992 | 15.432614988742 | | 1991 | 13.637999974286 | | 1990 | 13.86291850916 |
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