| Year | Value | | 2022 | 15.155129232701 | | 2021 | 14.813484635262 | | 2020 | 14.53167792479 | | 2019 | 14.467489523079 | | 2018 | 14.172832934789 | | 2017 | 13.893606504153 | | 2016 | 13.48021709276 | | 2015 | 13.101134893413 | | 2014 | 12.723316826395 | | 2013 | 12.546704997851 | | 2012 | 12.276109504142 | | 2011 | 12.122954292635 | | 2010 | 12.090496683571 | | 2009 | 12.041588971412 | | 2008 | 11.944748583433 | | 2007 | 11.958816019756 | | 2006 | 12.003708675026 | | 2005 | 11.982624197586 | | 2004 | 12.048010289759 | | 2003 | 11.672101740068 | | 2002 | 11.768471068131 | | 2001 | 11.698462155951 | | 2000 | 11.969948434036 | | 1999 | 12.094235870027 | | 1998 | 12.209047326496 | | 1997 | 12.321180129307 | | 1996 | 12.543110258141 | | 1995 | 12.733513378557 | | 1994 | 12.884315287587 | | 1993 | 12.953589251868 | | 1992 | 12.96621735089 | | 1991 | 12.924146057497 |
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