| Year | Value | | 2022 | 52.901444811523 | | 2021 | 52.948606148535 | | 2020 | 52.997387722555 | | 2019 | 53.045569861061 | | 2018 | 53.094360815435 | | 2017 | 53.144800898269 | | 2016 | 53.168276290711 | | 2015 | 53.168279799912 | | 2014 | 53.175973067412 | | 2013 | 53.187522379951 | | 2012 | 53.199841918061 | | 2011 | 53.212183404338 | | 2010 | 53.226149371524 | | 2009 | 53.24290001978 | | 2008 | 53.264070218069 | | 2007 | 53.290278662117 | | 2006 | 53.321153789027 | | 2005 | 53.301031322598 | | 2004 | 53.145812788177 | | 2003 | 52.89910451336 | | 2002 | 52.638729145397 | | 2001 | 52.367074800161 | | 2000 | 52.082996285807 | | 1999 | 51.787071577436 | | 1998 | 51.65119188431 | | 1997 | 51.693196675596 | | 1996 | 51.743833419536 | | 1995 | 51.796085954324 | | 1994 | 51.851283428615 | | 1993 | 51.909614889851 | | 1992 | 51.974561493486 | | 1991 | 52.039069243099 | | 1990 | 52.104605312638 | | 1989 | 52.157718817587 | | 1988 | 52.194967970952 | | 1987 | 52.22868103948 | | 1986 | 52.25913601295 | | 1985 | 52.286761549384 | | 1984 | 52.31078451182 | | 1983 | 52.332835562339 | | 1982 | 52.354246145983 | | 1981 | 52.372731493254 | | 1980 | 52.384426993404 | | 1979 | 52.387312436111 | | 1978 | 52.381564337706 | | 1977 | 52.369768350129 | | 1976 | 52.352939560968 | | 1975 | 52.331598863369 | | 1974 | 52.307227395685 | | 1973 | 52.278047301395 | | 1972 | 52.244553909403 | | 1971 | 52.207475140608 | | 1970 | 52.168327233066 | | 1969 | 52.123430673082 | | 1968 | 52.074601395206 | | 1967 | 52.026063337744 | | 1966 | 51.975845704551 | | 1965 | 51.923453982197 | | 1964 | 51.871130437594 | | 1963 | 51.817553731666 | | 1962 | 51.759726155336 | | 1961 | 51.710698415914 | | 1960 | 51.676262959515 |
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