| Year | Value | | 2022 | 1.7305450659253 | | 2021 | 1.863665826535 | | 2020 | 2.0095042982132 | | 2019 | 1.8355987142631 | | 2018 | 1.791444235003 | | 2017 | 1.7337551021894 | | 2016 | 1.4277045414779 | | 2015 | 1.4507182437678 | | 2014 | 1.3476637836228 | | 2013 | 1.2922307671482 | | 2012 | 1.1739252275223 | | 2011 | 1.2355686693178 | | 2010 | 1.2269766069761 | | 2009 | 1.2780696123372 | | 2008 | 1.3999843655816 | | 2007 | 1.4936182598133 | | 2006 | 1.8451254600123 | | 2005 | 2.0069936091199 | | 2004 | 2.0076575613192 | | 2003 | 2.0884871335488 | | 2002 | 2.2872960754766 | | 2001 | 2.4207451879196 | | 2000 | 2.4989141842602 | | 1999 | 2.6402592674038 | | 1998 | 3.0041748639189 | | 1997 | 3.0176499620052 | | 1996 | 2.3690729256338 | | 1995 | 2.6134476852881 | | 1994 | 3.114728408059 | | 1993 | 2.7406080146938 | | 1992 | 4.2476825168307 | | 1991 | 4.7733346643012 | | 1990 | 4.547415049251 | | 1989 | 4.7972961149151 | | 1988 | 4.2054706124654 | | 1987 | 3.9140286216301 | | 1986 | 4.4457111647215 | | 1985 | 4.2992808431191 | | 1984 | 1.9067272179183 | | 1983 | 1.9850871304954 | | 1982 | 2.0402158999359 | | 1981 | 2.2012235789042 | | 1980 | 2.2045426546584 |
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