| Year | Value | | 2022 | 6.0154521027122 | | 2021 | 7.1068045025446 | | 2020 | 7.2720632421164 | | 2019 | 6.7282321423865 | | 2018 | 6.9717378001227 | | 2017 | 7.4675176364021 | | 2016 | 8.0746695035943 | | 2015 | 8.498048886348 | | 2014 | 8.8791824856454 | | 2013 | 9.1956689511873 | | 2012 | 8.9965595922757 | | 2011 | 8.7978795370457 | | 2010 | 9.1333400203931 | | 2009 | 9.0592809848473 | | 2008 | 7.1417615692346 | | 2007 | 7.1712504621133 | | 2006 | 7.9046857754315 | | 2005 | 8.3478543906222 | | 2004 | 8.6861912323447 | | 2003 | 8.696451822035 | | 2002 | 8.7814195625746 | | 2001 | 8.8347228579525 | | 2000 | 9.2742269596578 | | 1999 | 10.389318259041 | | 1998 | 10.328170347576 | | 1997 | 10.160548230906 | | 1996 | 9.8440432110179 | | 1995 | 9.5138842460231 | | 1994 | 9.7751377698784 | | 1993 | 8.8356980330729 | | 1992 | 7.7113467659268 |
|