| Year | Value | | 2022 | 37.534741134063 | | 2021 | 37.268365446358 | | 2020 | 38.865946489485 | | 2019 | 39.132130133753 | | 2018 | 36.659597695273 | | 2017 | 36.376532626322 | | 2016 | 36.03068754986 | | 2015 | 35.754048825721 | | 2014 | 35.448217164105 | | 2013 | 35.26907972721 | | 2012 | 35.076536485058 | | 2011 | 34.879376841035 | | 2010 | 34.858306922724 | | 2009 | 34.570344447849 | | 2008 | 34.772849224041 | | 2007 | 34.510374757716 | | 2006 | 34.246698744731 | | 2005 | 33.954041544323 | | 2004 | 33.373458919378 | | 2003 | 33.08247882999 | | 2002 | 32.583444843828 | | 2001 | 32.129836776758 | | 2000 | 32.004902619417 | | 1999 | 31.620632284725 | | 1998 | 31.401553277037 | | 1997 | 31.349933701768 | | 1996 | 31.266483708954 | | 1995 | 31.216946621113 | | 1994 | 31.390376777129 | | 1993 | 31.424784181613 | | 1992 | 31.858824688812 | | 1991 | 32.147967683882 |
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