| Year | Value | | 2022 | 1.5848809238459 | | 2021 | 1.2208446612055 | | 2020 | 1.2984791156369 | | 2019 | 1.2808059620147 | | 2018 | 1.1605447850507 | | 2017 | 1.1091510055888 | | 2016 | 1.1035810088045 | | 2015 | 1.1623038643223 | | 2014 | 1.3465159912891 | | 2013 | 1.4089821014115 | | 2012 | 1.4870825765522 | | 2011 | 1.5282663377663 | | 2010 | 1.5585918930235 | | 2009 | 1.5172171395597 | | 2008 | 1.9848688566777 | | 2007 | 1.8207653435572 | | 2006 | 1.5677690887307 | | 2005 | 1.3500049705632 | | 2004 | 1.3811579421109 | | 2003 | 1.336842924198 | | 2002 | 1.320034494332 | | 2001 | 1.3092913747559 | | 2000 | 1.2463602418922 | | 1999 | 1.2492100988596 | | 1998 | 1.2382425606475 | | 1997 | 1.2830807803627 | | 1996 | 1.3790296273416 | | 1995 | 2.0535873590579 | | 1994 | 2.5478190603765 | | 1993 | 3.1994510667497 | | 1992 | 4.6708878237371 | | 1991 | 5.7912704218483 | | 1990 | 5.8883007196812 | | 1989 | 5.1676127235729 | | 1988 | 5.6173166284336 | | 1987 | 5.8622289226487 | | 1986 | 5.6261865040557 | | 1985 | 5.6514261993714 | | 1984 | 6.1175045427014 | | 1983 | 5.4412819899546 | | 1982 | 5.6515957446808 | | 1981 | 5.8483170534437 | | 1980 | 6.0520216327582 |
|