| Year | Value | | 2021 | 7.9776142064157 | | 2020 | 8.0638657095313 | | 2019 | 8.1501172126468 | | 2018 | 8.2363687157624 | | 2017 | 8.3226202188779 | | 2016 | 8.4088717219935 | | 2015 | 8.495123225109 | | 2014 | 8.5813722989469 | | 2013 | 8.6676213727848 | | 2012 | 8.7538704466227 | | 2011 | 8.8401195204606 | | 2010 | 8.9263685942985 | | 2009 | 9.0126193686307 | | 2008 | 9.098870142963 | | 2007 | 9.1851209172952 | | 2006 | 9.2713716916275 | | 2005 | 9.3576224659598 | | 2004 | 9.443873240292 | | 2003 | 9.5301240146242 | | 2002 | 9.6163747889565 | | 2001 | 9.7026255632888 | | 2000 | 9.788876337621 | | 1999 | 9.8751261402422 | | 1998 | 9.9613759428634 | | 1997 | 10.047625745485 | | 1996 | 10.133875548106 | | 1995 | 10.220125350727 | | 1994 | 10.306375153348 | | 1993 | 10.392624955969 | | 1992 | 10.47887475859 | | 1991 | 10.565124561212 | | 1990 | 10.651374363833 |
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