| Year | Value | | 2022 | 50.444587984112 | | 2021 | 50.481755964229 | | 2020 | 50.535778151853 | | 2019 | 50.612827219879 | | 2018 | 50.715684210181 | | 2017 | 50.837998609435 | | 2016 | 50.998521764494 | | 2015 | 51.184560513635 | | 2014 | 51.291315715429 | | 2013 | 51.319710808683 | | 2012 | 51.349641146158 | | 2011 | 51.382485472078 | | 2010 | 51.419476035982 | | 2009 | 51.457787728845 | | 2008 | 51.494982667181 | | 2007 | 51.529062978816 | | 2006 | 51.558460857727 | | 2005 | 51.580504582792 | | 2004 | 51.596975117642 | | 2003 | 51.611324602095 | | 2002 | 51.621305886282 | | 2001 | 51.635373490792 | | 2000 | 51.659060219528 | | 1999 | 51.682740942013 | | 1998 | 51.704208387321 | | 1997 | 51.726119642865 | | 1996 | 51.745583354544 | | 1995 | 51.763508496811 | | 1994 | 51.777480776279 | | 1993 | 51.789232230594 | | 1992 | 51.799018001845 | | 1991 | 51.817151548541 | | 1990 | 51.851750413548 | | 1989 | 51.889721237285 | | 1988 | 51.930396161123 | | 1987 | 51.976674239761 | | 1986 | 52.027409505902 | | 1985 | 52.084287120947 | | 1984 | 52.146661158099 | | 1983 | 52.214813088379 | | 1982 | 52.295425667278 | | 1981 | 52.390084457137 | | 1980 | 52.494686542504 | | 1979 | 52.594374737662 | | 1978 | 52.676399160148 | | 1977 | 52.747951877339 | | 1976 | 52.819671756272 | | 1975 | 52.891532768088 | | 1974 | 52.961879233887 | | 1973 | 53.030910923413 | | 1972 | 53.0991329087 | | 1971 | 53.191362356615 | | 1970 | 53.287163663236 | | 1969 | 53.359763946703 | | 1968 | 53.431346670042 | | 1967 | 53.503129693352 | | 1966 | 53.574650277163 | | 1965 | 53.645641824583 | | 1964 | 53.713781876902 | | 1963 | 53.779000730866 | | 1962 | 53.839696451803 | | 1961 | 53.895511806347 | | 1960 | 53.956252032185 |
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