| Year | Value | | 2022 | 32.899581032104 | | 2021 | 32.402908037893 | | 2020 | 32.000757804619 | | 2019 | 31.797553918196 | | 2018 | 31.870331517879 | | 2017 | 31.821495434259 | | 2016 | 31.814630163766 | | 2015 | 32.030987890864 | | 2014 | 33.095557785182 | | 2013 | 33.486758149006 | | 2012 | 33.30839704141 | | 2011 | 31.712291799115 | | 2010 | 31.944752336394 | | 2009 | 32.432390996575 | | 2008 | 32.479436307771 | | 2007 | 32.558620879027 | | 2006 | 32.172238629592 | | 2005 | 31.930188168868 | | 2004 | 31.464558035612 | | 2003 | 31.074897298195 | | 2002 | 30.563969045696 | | 2001 | 30.965727802482 | | 2000 | 31.586035921424 | | 1999 | 31.124319586943 | | 1998 | 30.988667745629 | | 1997 | 31.519828829783 | | 1996 | 32.186634868205 | | 1995 | 32.911138609243 | | 1994 | 33.511249576789 | | 1993 | 34.177545877414 | | 1992 | 34.930165334283 | | 1991 | 35.194399237376 |
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