| Year | Value | | 2023 | 4.6021031480828 | | 2022 | 3.7995364122613 | | 2021 | 4.9305174071276 | | 2020 | 5.2415260250682 | | 2019 | 3.8490186357853 | | 2018 | 3.5492933126904 | | 2017 | 3.7563017324966 | | 2016 | 3.6885273031781 | | 2015 | 5.4648767929386 | | 2014 | 4.5550131239822 | | 2013 | 4.5409233096147 | | 2012 | 4.6586182519632 | | 2011 | 4.6701355554702 | | 2010 | 2.7910043565289 | | 2009 | 3.3254216816707 | | 2008 | 3.29121114577 | | 2007 | 2.8641949189894 | | 2006 | 3.4177593325581 | | 2005 | 2.2990696745858 | | 2004 | 2.6294811376052 | | 2003 | 2.4263625550969 | | 2002 | 2.2433137703177 | | 2001 | 2.3120626081722 | | 2000 | 2.2678620631186 | | 1999 | 2.6251099314452 | | 1998 | 2.4123559125972 | | 1997 | 2.3240497992578 | | 1996 | 2.2542303413549 | | 1995 | 2.73690130284 | | 1994 | 1.946584590385 | | 1993 | 5.0004677856961 | | 1992 | 2.4002256212084 |
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