| Year | Value | | 2022 | 1.5721347042386 | | 2021 | 1.7391258895814 | | 2020 | 1.4021704205015 | | 2019 | 1.5311342419431 | | 2018 | 1.6669275682647 | | 2017 | 1.4710625174298 | | 2016 | 1.602097453639 | | 2015 | 1.2090991706832 | | 2014 | 1.2133660029387 | | 2013 | 1.2517012560332 | | 2012 | 1.1134795947635 | | 2011 | 1.2938601595448 | | 2010 | 1.2153093310459 | | 2009 | 1.3358758760969 | | 2008 | 1.2919668687193 | | 2007 | 1.3795917338401 | | 2006 | 1.2710568703227 | | 2005 | 1.1304645291005 | | 2004 | 1.0578248701437 | | 2003 | 1.1154427782623 | | 2002 | 1.1012404361718 | | 2001 | 1.1156674925052 | | 2000 | 1.0483602770516 | | 1999 | 1.2021268051452 | | 1998 | 1.1791418545261 | | 1997 | 1.1969122297618 | | 1996 | 1.2439179373703 | | 1995 | 1.3100991106619 | | 1994 | 1.3476197380418 | | 1993 | 1.668304044287 | | 1992 | 1.4439999325024 | | 1991 | 1.5470555665156 | | 1990 | 1.6334689857387 | | 1989 | 2.0276962348437 | | 1988 | 2.1117845117845 | | 1987 | 1.9811881188119 | | 1986 | 2.0400413507926 | | 1985 | 2.1928625093914 | | 1984 | 2.4079526226734 | | 1983 | 2.5458845789972 | | 1982 | 2.3495107632094 | | 1981 | 2.7344148319815 | | 1980 | 2.7552702702703 | | 1979 | 3.4311346548189 |
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