| Year | Value | | 2022 | 15.353809149565 | | 2021 | 14.446904541807 | | 2020 | 14.055500706241 | | 2019 | 14.90052462326 | | 2018 | 14.609842448027 | | 2017 | 14.850818408179 | | 2016 | 14.385212929851 | | 2015 | 15.797262655066 | | 2014 | 15.699748372001 | | 2013 | 14.022114346451 | | 2012 | 13.226990714276 | | 2011 | 14.575881186967 | | 2010 | 12.142165202367 | | 2009 | 12.675227384195 | | 2008 | 13.031511014491 | | 2003 | 11.258826863848 | | 2000 | 11.219754185325 | | 1999 | 13.476921281862 | | 1998 | 13.743732154452 |
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