| Year | Value | | 2022 | 2.0996423245601 | | 2021 | 2.3473424641744 | | 2020 | 2.450642976184 | | 2019 | 2.1964813035577 | | 2018 | 2.2084424288968 | | 2017 | 2.0673557269102 | | 2016 | 1.9098836302185 | | 2015 | 1.8016226206537 | | 2014 | 1.6567948792676 | | 2013 | 1.5758960136437 | | 2012 | 1.5479398218095 | | 2011 | 1.4977887080703 | | 2010 | 1.4930968809097 | | 2009 | 1.3131279988524 | | 2008 | 0.79821750779099 | | 2007 | 0.9146120282239 | | 2006 | 1.0431000795266 | | 2005 | 1.1275790712475 | | 2004 | 1.2967422117536 | | 2003 | 1.4475188506946 | | 2002 | 1.5196174052465 | | 2001 | 1.7748105314437 | | 2000 | 2.2098132098356 | | 1999 | 2.5100290817204 | | 1998 | 2.6620478997978 | | 1997 | 3.0033611623116 | | 1996 | 3.2384545833913 | | 1995 | 3.5773105786184 | | 1994 | 3.8423429002511 | | 1993 | 1.7612894987517 | | 1992 | 3.1459330143541 | | 1991 | 2.3278965845041 | | 1990 | 2.07137559385 | | 1989 | 1.992453582058 | | 1988 | 1.2782035615864 | | 1987 | 1.5742453461372 | | 1986 | 1.1468508824006 |
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