| Year | Value | | 2023 | 60.226 | | 2022 | 59.88 | | 2021 | 57.717 | | 2020 | 59.091 | | 2019 | 58.83 | | 2018 | 58.852 | | 2017 | 58.304 | | 2016 | 57.94 | | 2015 | 57.33 | | 2014 | 56.569 | | 2013 | 55.397 | | 2012 | 54.066 | | 2011 | 52.508 | | 2010 | 51.197 | | 2009 | 49.245 | | 2008 | 48.246 | | 2007 | 47.644 | | 2006 | 46.856 | | 2005 | 46.198 | | 2004 | 45.655 | | 2003 | 44.987 | | 2002 | 45.135 | | 2001 | 43.997 | | 2000 | 44.834 | | 1999 | 45.031 | | 1998 | 46.024 | | 1997 | 47.001 | | 1996 | 46.94 | | 1995 | 49.181 | | 1994 | 50.402 | | 1993 | 51.629 | | 1992 | 52.908 | | 1991 | 54.098 | | 1990 | 55.161 | | 1989 | 56.062 | | 1988 | 56.754 | | 1987 | 57.193 | | 1986 | 57.518 | | 1985 | 57.51 | | 1984 | 57.345 | | 1983 | 56.721 | | 1982 | 56.75 | | 1981 | 56.397 | | 1980 | 56.177 | | 1979 | 49.153 | | 1978 | 49.017 | | 1977 | 52.972 | | 1976 | 54.168 |
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