| Year | Value | | 2023 | 71.388 | | 2022 | 70.319 | | 2021 | 69.17 | | 2020 | 69.805 | | 2019 | 70.061 | | 2018 | 69.883 | | 2017 | 70.122 | | 2016 | 69.961 | | 2015 | 69.708 | | 2014 | 70.038 | | 2013 | 69.909 | | 2012 | 69.609 | | 2011 | 69.397 | | 2010 | 69.143 | | 2009 | 68.812 | | 2008 | 68.488 | | 2007 | 68.121 | | 2006 | 67.679 | | 2005 | 67.234 | | 2004 | 66.731 | | 2003 | 66.284 | | 2002 | 65.669 | | 2001 | 65.098 | | 2000 | 64.616 | | 1999 | 64.161 | | 1998 | 63.708 | | 1997 | 63.292 | | 1996 | 62.836 | | 1995 | 62.468 | | 1994 | 62.011 | | 1993 | 61.616 | | 1992 | 61.194 | | 1991 | 60.764 | | 1990 | 60.288 | | 1989 | 59.822 | | 1988 | 59.2 | | 1987 | 58.652 | | 1986 | 57.761 | | 1985 | 57.257 | | 1984 | 56.453 | | 1983 | 55.54 | | 1982 | 54.28 | | 1981 | 53.685 | | 1980 | 52.671 | | 1979 | 51.613 | | 1978 | 50.622 | | 1977 | 49.569 | | 1976 | 48.575 | | 1975 | 47.66 |
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