| Year | Value | | 2022 | 1.6017107992987 | | 2021 | 1.6251013894252 | | 2020 | 1.7919571474799 | | 2019 | 1.7131385883127 | | 2018 | 1.6899068065192 | | 2017 | 1.7425225650877 | | 2016 | 1.8287767652456 | | 2015 | 1.8362754572617 | | 2014 | 1.8353123569733 | | 2013 | 1.8254865090273 | | 2012 | 1.7660239515648 | | 2011 | 1.6971273690654 | | 2010 | 1.7560856437008 | | 2009 | 1.9029637147451 | | 2008 | 1.7249752059512 | | 2007 | 1.6990955752763 | | 2006 | 1.7018167421276 | | 2005 | 1.7225319159716 | | 2004 | 1.7446198341456 | | 2003 | 1.8263031377831 | | 2002 | 1.8596371046787 | | 2001 | 1.7715473439336 | | 2000 | 1.690183816328 | | 1999 | 1.7396005271256 | | 1998 | 1.6837071785604 | | 1997 | 1.8615279083653 | | 1996 | 1.9227200211039 | | 1995 | 1.9989090972658 | | 1994 | 2.0769437358594 | | 1993 | 2.1168238333811 | | 1992 | 2.3495922249206 | | 1991 | 2.003241613345 | | 1990 | 2.2102968251894 | | 1989 | 2.3591813985318 | | 1981 | 2.6363522055416 |
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