| Year | Value | | 2021 | 28.79197080292 | | 2020 | 28.79197080292 | | 2019 | 28.79197080292 | | 2018 | 28.79197080292 | | 2017 | 28.792062043796 | | 2016 | 28.802189781022 | | 2015 | 28.80246350365 | | 2014 | 28.750510948905 | | 2013 | 28.698558394161 | | 2012 | 28.646605839416 | | 2011 | 28.594653284672 | | 2010 | 28.542700729927 | | 2009 | 28.496094890511 | | 2008 | 28.449489051095 | | 2007 | 28.402883211679 | | 2006 | 28.356277372263 | | 2005 | 28.309671532847 | | 2004 | 28.263065693431 | | 2003 | 28.216459854015 | | 2002 | 28.169854014598 | | 2001 | 28.123248175182 | | 2000 | 28.076642335766 | | 1999 | 28.147810218978 | | 1998 | 28.21897810219 | | 1997 | 28.290145985402 | | 1996 | 28.361313868613 | | 1995 | 28.432481751825 | | 1994 | 28.503649635036 | | 1993 | 28.574817518248 | | 1992 | 28.64598540146 | | 1991 | 28.717153284672 | | 1990 | 28.788321167883 |
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