| Year | Value | | 2022 | 14.382278402879 | | 2021 | 14.060791166547 | | 2020 | 13.80163781046 | | 2019 | 13.735118542007 | | 2018 | 13.49327791559 | | 2017 | 13.197833464864 | | 2016 | 12.862467938856 | | 2015 | 12.527310628027 | | 2014 | 12.13205835195 | | 2013 | 11.214234997365 | | 2012 | 10.374465984544 | | 2011 | 9.5489145286451 | | 2010 | 8.7450437172625 | | 2009 | 7.9845939127634 | | 2008 | 7.404822111558 | | 2007 | 6.7324959605238 | | 2006 | 6.188532256226 | | 2005 | 5.9039407751779 | | 2004 | 5.6116015732612 | | 2003 | 5.4159176563664 | | 2002 | 5.1950475669359 | | 2001 | 5.0589950079974 | | 2000 | 4.9024875910061 | | 1999 | 4.8215627608128 | | 1998 | 4.7592677580022 | | 1997 | 4.6341613750015 | | 1996 | 4.5491356775903 | | 1995 | 4.4678786949694 | | 1994 | 4.4500560810879 | | 1993 | 4.3948371932772 | | 1992 | 4.3730613128994 | | 1991 | 4.3578042082127 |
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