| Year | Value | | 2021 | 52.347780738053 | | 2020 | 52.413015135196 | | 2019 | 52.459611133156 | | 2018 | 52.534164729891 | | 2017 | 52.636675925401 | | 2016 | 52.767144719687 | | 2015 | 52.925571112749 | | 2014 | 53.111955104586 | | 2013 | 53.298339096423 | | 2012 | 53.48472308826 | | 2011 | 53.671107080097 | | 2010 | 53.857491071935 | | 2009 | 54.044101808288 | | 2008 | 54.23071254464 | | 2007 | 54.417323280993 | | 2006 | 54.603934017346 | | 2005 | 54.790544753699 | | 2004 | 54.977155490052 | | 2003 | 55.163766226404 | | 2002 | 55.350376962757 | | 2001 | 55.53698769911 | | 2000 | 55.723598435463 | | 1999 | 56.049543676662 | | 1998 | 56.375488917862 | | 1997 | 56.701434159061 | | 1996 | 57.027379400261 | | 1995 | 57.35332464146 | | 1994 | 57.67926988266 | | 1993 | 58.005215123859 | | 1992 | 58.331160365059 | | 1991 | 58.657105606258 | | 1990 | 58.983050847458 |
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