| Year | Value | | 2022 | 5.8860205589821 | | 2021 | 7.3007041729501 | | 2020 | 7.6287691623948 | | 2019 | 7.4382882009657 | | 2018 | 7.2836570115311 | | 2017 | 7.3780579562712 | | 2016 | 7.590264811978 | | 2015 | 7.4406636956321 | | 2014 | 7.2869768846869 | | 2013 | 7.2018712653088 | | 2012 | 7.1930626316309 | | 2011 | 7.8394944879311 | | 2010 | 8.7099047682602 | | 2009 | 9.3720959693008 | | 2008 | 7.4386148597303 | | 2007 | 7.2853473119638 | | 2006 | 7.615739411961 | | 2005 | 7.6201085761766 | | 2004 | 8.2058650131259 | | 2003 | 8.5288117420468 | | 2002 | 8.5638240074448 | | 2001 | 9.3504982171573 | | 2000 | 9.6557208700472 | | 1999 | 11.88274348002 | | 1998 | 11.276793315254 | | 1997 | 10.123074697466 | | 1996 | 8.7981473564981 | | 1995 | 7.9658525831106 | | 1994 | 7.5177474655809 | | 1993 | 5.9806254116335 | | 1992 | 5.4002009617047 |
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