| Year | Value | | 2024 | 53.859629294756 | | 2023 | 53.900829243527 | | 2022 | 53.938847908103 | | 2021 | 53.989765506382 | | 2020 | 54.046762589928 | | 2019 | 54.017305315204 | | 2018 | 53.878971595374 | | 2017 | 53.739052324276 | | 2016 | 53.613171499213 | | 2015 | 53.466516601013 | | 2014 | 53.211785956198 | | 2013 | 52.906844968268 | | 2012 | 52.83422459893 | | 2011 | 52.984455385296 | | 2010 | 53.120243531202 | | 2009 | 53.233564938536 | | 2008 | 53.3378925772 | | 2007 | 53.445238835354 | | 2006 | 53.570152605522 | | 2005 | 53.718841457261 | | 2004 | 53.917562181525 | | 2003 | 54.12004069176 | | 2002 | 54.294211147003 | | 2001 | 54.459487391484 | | 2000 | 54.562519553655 | | 1999 | 54.46272683985 | | 1998 | 54.210753616929 | | 1997 | 53.954053457036 | | 1996 | 53.698878441146 | | 1995 | 53.582645108759 | | 1994 | 53.601669648181 | | 1993 | 53.634253603714 | | 1992 | 53.680655450622 | | 1991 | 53.733828615345 | | 1990 | 53.807838510945 | | 1989 | 53.78387420542 | | 1988 | 53.653373395247 | | 1987 | 53.509139109809 | | 1986 | 53.344266970907 | | 1985 | 53.115640295127 | | 1984 | 52.834433113377 | | 1983 | 52.575734276488 | | 1982 | 52.292421616512 | | 1981 | 52.031930333817 | | 1980 | 51.870263222231 | | 1979 | 51.868363459512 | | 1978 | 51.953376205788 | | 1977 | 52.019798818458 | | 1976 | 52.0517501389 | | 1975 | 52.102102102102 |
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