| Year | Value | | 2022 | 51.221222058502 | | 2021 | 51.181034979024 | | 2020 | 51.120411924281 | | 2019 | 51.083601654874 | | 2018 | 51.065822392224 | | 2017 | 51.052604860247 | | 2016 | 51.045086933202 | | 2015 | 51.040509839139 | | 2014 | 51.037912756275 | | 2013 | 51.038000579176 | | 2012 | 51.039981898462 | | 2011 | 51.045258407628 | | 2010 | 51.048402495207 | | 2009 | 51.045497505849 | | 2008 | 51.042031111619 | | 2007 | 51.040758594873 | | 2006 | 51.04194073 | | 2005 | 51.045027407475 | | 2004 | 51.050226525238 | | 2003 | 51.056411658452 | | 2002 | 51.062440064036 | | 2001 | 51.06807344905 | | 2000 | 51.059185187336 | | 1999 | 51.037139119286 | | 1998 | 51.016226232673 | | 1997 | 50.993936732773 | | 1996 | 50.968560832974 | | 1995 | 50.940813634192 | | 1994 | 50.913973010796 | | 1993 | 50.886528872237 | | 1992 | 50.857018336204 | | 1991 | 50.825264951438 | | 1990 | 50.794594467861 | | 1989 | 50.762862894516 | | 1988 | 50.726586207742 | | 1987 | 50.68935376537 | | 1986 | 50.650131358916 | | 1985 | 50.610686188908 | | 1984 | 50.570843618341 | | 1983 | 50.529879796577 | | 1982 | 50.487113176381 | | 1981 | 50.441928129032 | | 1980 | 50.396123274811 | | 1979 | 50.349513145638 | | 1978 | 50.30251623273 | | 1977 | 50.258175446041 | | 1976 | 50.198191000832 | | 1975 | 50.125582955408 | | 1974 | 50.058701349422 | | 1973 | 49.992508356645 | | 1972 | 49.925131812609 | | 1971 | 49.849992316611 | | 1970 | 49.804861097109 | | 1969 | 49.797437693672 | | 1968 | 49.790727592215 | | 1967 | 49.78404279759 | | 1966 | 49.777126468894 | | 1965 | 49.769494312449 | | 1964 | 49.760787023177 | | 1963 | 49.750708554259 | | 1962 | 49.738885916172 | | 1961 | 49.725263417599 | | 1960 | 49.710173319192 |
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