| Year | Value | | 2024 | 36.807751759659 | | 2023 | 36.570797983651 | | 2022 | 36.322631030829 | | 2021 | 36.070495125631 | | 2020 | 35.70256045803 | | 2019 | 34.906756173202 | | 2018 | 34.210604581086 | | 2017 | 33.558691252217 | | 2016 | 32.951200800524 | | 2015 | 32.38831787027 | | 2014 | 31.862616218092 | | 2013 | 31.442718794421 | | 2012 | 31.203183985863 | | 2011 | 30.923738946703 | | 2010 | 30.623284830533 | | 2009 | 30.303150224821 | | 2008 | 29.964663717033 | | 2007 | 29.609153894637 | | 2006 | 29.237949345098 | | 2005 | 28.852378655883 | | 2004 | 28.450652375481 | | 2003 | 28.027706145561 | | 2002 | 27.577761926861 | | 2001 | 27.103360305355 | | 2000 | 26.605485938323 | | 1999 | 26.085123483048 | | 1998 | 25.543257596812 | | 1997 | 24.980872936896 | | 1996 | 24.398954160581 | | 1995 | 23.798485925151 | | 1994 | 23.170080244396 | | 1993 | 22.492355564129 | | 1992 | 21.756952584616 | | 1991 | 20.982248759941 | | 1990 | 20.182053172185 | | 1989 | 19.370174903432 | | 1988 | 18.560423035763 | | 1987 | 17.766606651262 | | 1986 | 17.006711812525 | | 1985 | 16.268084173822 | | 1984 | 15.51393061342 | | 1983 | 14.740188333574 | | 1982 | 13.953716751329 | | 1981 | 13.161375283728 | | 1980 | 12.370023347814 | | 1979 | 11.586520360629 | | 1978 | 10.817725739217 | | 1977 | 10.070498900621 | | 1976 | 9.3516992618847 |
|