| Year | Value | | 2021 | 6.1935589471169 | | 2020 | 6.6974297622194 | | 2019 | 5.8672024536599 | | 2018 | 5.9461946310889 | | 2017 | 5.587845921137 | | 2014 | 5.584122148651 | | 2013 | 5.6244338846603 | | 2012 | 5.4218175400467 | | 2011 | 5.8893813459049 | | 2010 | 5.4672982575677 | | 2009 | 6.3067405611865 | | 2005 | 6.5654438629014 | | 2003 | 6.4274708057073 | | 2000 | 5.5262590576075 | | 1999 | 6.205448536961 | | 1996 | 5.6347277057362 | | 1994 | 5.6765476677242 |
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