| Year | Value | | 2022 | 0.70258759941972 | | 2021 | 0.74178636312329 | | 2020 | 0.88658404487493 | | 2019 | 0.72856374355152 | | 2018 | 0.71892819047635 | | 2017 | 0.86519137622199 | | 2016 | 0.79222021349685 | | 2015 | 0.88226673448124 | | 2014 | 0.77785517823283 | | 2013 | 0.91876983918307 | | 2012 | 0.71154947340638 | | 2011 | 0.65377670260681 | | 2010 | 0.61758709195193 | | 2009 | 0.57113389199642 | | 2008 | 0.57894580449339 | | 2007 | 0.71236193115127 | | 2006 | 0.65870277762871 | | 2005 | 0.75078939400493 | | 2004 | 0.94571462172722 | | 2003 | 0.90928503677365 | | 2002 | 0.70012020880104 | | 2001 | 0.57279265270421 | | 2000 | 0.68448376350044 | | 1999 | 0.81081265401508 | | 1998 | 1.0191168438741 | | 1997 | 1.4977417376274 | | 1996 | 1.2643925282781 | | 1995 | 1.2263098606424 | | 1994 | 1.2661556171838 | | 1993 | 1.223557808937 | | 1992 | 1.3568760070115 | | 1991 | 1.3240641839588 | | 1990 | 1.4104929196741 | | 1989 | 1.3891363413656 | | 1988 | 1.5308410589377 | | 1987 | 1.7221876700614 | | 1986 | 2.0097653956295 | | 1985 | 2.170599353698 | | 1984 | 2.2854202592201 | | 1983 | 2.3981294204037 | | 1982 | 2.9019282697113 | | 1981 | 2.8846220014038 | | 1980 | 2.9172176905626 | | 1979 | 3.0202589194827 | | 1978 | 3.1631935285325 | | 1977 | 3.2060892023965 | | 1976 | 3.4218676252853 | | 1975 | 3.4921890448883 | | 1974 | 2.7059208068734 |
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