| Year | Value | | 2021 | 21.434540389972 | | 2020 | 21.685236768802 | | 2019 | 21.997206703911 | | 2018 | 22.310924369748 | | 2017 | 22.626404494382 | | 2016 | 22.969675599436 | | 2015 | 23.231875881523 | | 2014 | 23.589844851904 | | 2013 | 24.015558698727 | | 2012 | 24.409065155807 | | 2011 | 24.838920454546 | | 2010 | 25.271225071225 | | 2009 | 25.239571428571 | | 2008 | 25.135714285714 | | 2007 | 25.211942446043 | | 2006 | 25.143515850144 | | 2005 | 25.220464441219 | | 2004 | 25.114949201742 | | 2003 | 25.082241630277 | | 2002 | 25.420444444444 | | 2001 | 25.501641791045 | | 2000 | 25.393283582089 | | 1999 | 25.066865671642 | | 1998 | 24.740597014925 | | 1997 | 24.414179104478 | | 1996 | 24.087910447761 | | 1995 | 23.761492537313 | | 1994 | 23.435074626866 | | 1993 | 23.108805970149 | | 1992 | 22.782388059701 | | 1991 | 22.456119402985 | | 1990 | 22.129701492537 |
|