| Year | Value | | 2022 | 1.5257372069076 | | 2021 | 1.6833660885555 | | 2020 | 1.7605738102229 | | 2019 | 1.3355019440396 | | 2018 | 1.0060748018113 | | 2017 | 1.1935528970937 | | 2016 | 1.0020199042905 | | 2015 | 0.90472207333615 | | 2014 | 0.85780963079475 | | 2013 | 0.9434037793281 | | 2012 | 1.0264985611604 | | 2011 | 1.0370905637293 | | 2010 | 1.0219903567363 | | 2009 | 1.125985152169 | | 2008 | 1.1797675620911 | | 2007 | 1.2672142512568 | | 2006 | 1.2185665067282 | | 2005 | 1.4098361555401 | | 2004 | 1.472723818891 | | 2003 | 1.6426215943869 | | 2002 | 1.5937738020926 | | 2001 | 1.5701270901466 | | 2000 | 1.51310022701 | | 1999 | 1.4336125996918 | | 1998 | 1.2721641748015 | | 1997 | 1.4766844027823 | | 1996 | 1.2590610397978 | | 1995 | 1.3247274830333 | | 1994 | 1.8241343838563 | | 1993 | 1.9065682898097 | | 1992 | 2.1796531721192 | | 1991 | 2.1614697994636 | | 1990 | 2.5635380270904 | | 1989 | 2.7861620617599 | | 1988 | 3.5962232713135 | | 1987 | 3.1555772994129 | | 1986 | 3.2237325495959 | | 1985 | 4.9724291380478 | | 1984 | 3.1476750127747 | | 1983 | 3.335936628361 | | 1982 | 3.2433069937493 | | 1981 | 3.3337607385562 | | 1980 | 3.3425797503467 | | 1979 | 3.2390444086179 | | 1978 | 3.2396379228204 | | 1977 | 2.9553264604811 | | 1976 | 3.0062393647192 | | 1975 | 3.3354050134659 | | 1974 | 3.2078413900646 | | 1973 | 3.006993006993 | | 1972 | 3.2736572890026 | | 1971 | 3.7416851441242 | | 1970 | 4.0300751879699 |
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