| Year | Value | | 2022 | 50.277278250647 | | 2021 | 50.287964037671 | | 2020 | 50.30600131646 | | 2019 | 50.332135037179 | | 2018 | 50.368224805638 | | 2017 | 50.412649453735 | | 2016 | 50.472045166244 | | 2015 | 50.54273052934 | | 2014 | 50.583770483419 | | 2013 | 50.593479324475 | | 2012 | 50.603057778745 | | 2011 | 50.613518630319 | | 2010 | 50.62515799402 | | 2009 | 50.635721617531 | | 2008 | 50.644888726853 | | 2007 | 50.653657934642 | | 2006 | 50.660774400385 | | 2005 | 50.666643793413 | | 2004 | 50.671974654178 | | 2003 | 50.675469822056 | | 2002 | 50.676514647601 | | 2001 | 50.67675282587 | | 2000 | 50.679883684117 | | 1999 | 50.685323740437 | | 1998 | 50.689924003094 | | 1997 | 50.695517246652 | | 1996 | 50.702072732767 | | 1995 | 50.70767468553 | | 1994 | 50.711016484161 | | 1993 | 50.714849079153 | | 1992 | 50.723559966204 | | 1991 | 50.73403418613 | | 1990 | 50.742490565851 | | 1989 | 50.748815484742 | | 1988 | 50.75986767047 | | 1987 | 50.778254729255 | | 1986 | 50.794123281794 | | 1985 | 50.807185483771 | | 1984 | 50.821327625213 | | 1983 | 50.838980268743 | | 1982 | 50.857301886069 | | 1981 | 50.874230095354 | | 1980 | 50.862714565247 | | 1979 | 50.856368849519 | | 1978 | 50.896479623745 | | 1977 | 50.936392468471 | | 1976 | 50.961836942168 | | 1975 | 50.979417805378 | | 1974 | 50.994074900959 | | 1973 | 51.007400607111 | | 1972 | 51.02178650982 | | 1971 | 51.047364490879 | | 1970 | 51.07490342844 | | 1969 | 51.095907632191 | | 1968 | 51.120338933899 | | 1967 | 51.147132153098 | | 1966 | 51.170091564021 | | 1965 | 51.188986863835 | | 1964 | 51.209217151641 | | 1963 | 51.229402310631 | | 1962 | 51.248170164424 | | 1961 | 51.271749708972 | | 1960 | 51.303116876817 |
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