| Year | Value | | 2022 | 1.5081234547461 | | 2021 | 1.5171316098363 | | 2020 | 1.5926554164585 | | 2019 | 3.1321629747372 | | 2018 | 1.4486509045142 | | 2017 | 1.2215224547801 | | 2016 | 1.2433105098495 | | 2015 | 1.2455391200568 | | 2014 | 1.3095615665118 | | 2013 | 1.4542479726251 | | 2012 | 1.329769454397 | | 2011 | 1.3140305451208 | | 2010 | 1.6426791659148 | | 2009 | 1.7395115006238 | | 2008 | 2.1318639825753 | | 2007 | 2.2285399009753 | | 2006 | 2.0817619077714 | | 2005 | 2.2353502672637 | | 2004 | 2.3737116819405 | | 2003 | 2.6912014716123 | | 2002 | 2.7796765548401 | | 2001 | 2.8625195438764 | | 2000 | 2.652455761589 | | 1999 | 2.6451719563385 | | 1998 | 2.4530591474315 | | 1997 | 2.4307013549238 | | 1996 | 2.4029341090173 | | 1995 | 2.3741312837803 | | 1994 | 2.4926172862057 | | 1993 | 2.6092716117939 | | 1992 | 2.9726338432122 | | 1991 | 3.0432315729749 | | 1990 | 3.8334434897554 | | 1989 | 4.39627074964 |
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