| Year | Value | | 2020 | 1.2444407675991 | | 2019 | 1.2489050093404 | | 2018 | 1.2555036441391 | | 2017 | 1.3379872676378 | | 2016 | 1.3950100178177 | | 2015 | 1.4300651924944 | | 2014 | 1.3727846976153 | | 2013 | 1.687845201874 | | 2012 | 1.7417011186452 | | 2011 | 1.6971376305185 | | 2010 | 1.7336298562733 | | 2009 | 1.7713694325082 | | 2008 | 1.8158186684099 | | 2007 | 1.8791566435545 | | 2006 | 1.8788601521379 | | 2005 | 1.686007582217 | | 2004 | 1.6765550541231 | | 2003 | 1.7309795376014 | | 2002 | 1.7710159048071 | | 2001 | 1.8110647608774 | | 2000 | 1.8788046807071 | | 1999 | 1.8836499723677 | | 1998 | 1.9649930640755 | | 1997 | 2.0209063621911 | | 1996 | 1.8838363607455 | | 1995 | 1.9330256374687 | | 1994 | 0.86710500889402 | | 1993 | 1.0181983870465 | | 1992 | 1.0453061832474 | | 1991 | 1.1019151284933 |
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