| Year | Value | | 2024 | 22.833507077172 | | 2023 | 22.874012770368 | | 2022 | 22.894393920898 | | 2021 | 22.901229858398 | | 2020 | 22.891967773438 | | 2019 | 22.927177429199 | | 2018 | 22.984367370606 | | 2017 | 23.039672851562 | | 2016 | 23.088417053223 | | 2015 | 23.12971496582 | | 2014 | 23.155754089356 | | 2013 | 23.18359375 | | 2012 | 23.222307993316 | | 2011 | 23.292336097212 | | 2010 | 23.390086753131 | | 2009 | 23.506974812887 | | 2008 | 23.634538624237 | | 2007 | 23.764316534941 | | 2006 | 23.88784689276 | | 2005 | 23.996668045451 | | 2004 | 24.082318340774 | | 2003 | 24.136336126489 | | 2002 | 24.14851088875 | | 2001 | 24.112434387207 | | 2000 | 24.364616394043 | | 1999 | 24.618316650391 | | 1998 | 24.689987182617 | | 1997 | 24.932365417481 | | 1996 | 25.215950012207 | | 1995 | 25.416770935059 | | 1994 | 25.491561889648 | | 1993 | 25.505134582519 | | 1992 | 25.585906982422 | | 1991 | 25.85514831543 | | 1990 | 26.272010803223 | | 1989 | 26.746620178223 | | 1988 | 27.32186126709 | | 1987 | 27.85408782959 | | 1986 | 28.422571869608 | | 1985 | 28.928115844727 | | 1984 | 29.179870605469 | | 1983 | 29.740127563477 | | 1982 | 30.476585388184 | | 1981 | 31.079261404655 | | 1980 | 31.594100952148 | | 1979 | 32.284087332021 | | 1978 | 33.121256512516 | | 1977 | 34.060709652821 | | 1976 | 35.057547912126 |
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