| Year | Value | | 2022 | 49.602425628809 | | 2021 | 49.627733458475 | | 2020 | 49.666673706904 | | 2019 | 49.713622678474 | | 2018 | 49.765240106126 | | 2017 | 49.819798591993 | | 2016 | 49.875935831241 | | 2015 | 49.932000581967 | | 2014 | 49.987289058906 | | 2013 | 50.041797371979 | | 2012 | 50.096886904513 | | 2011 | 50.149154127833 | | 2010 | 50.198103142822 | | 2009 | 50.245666975545 | | 2008 | 50.291566907072 | | 2007 | 50.336971665616 | | 2006 | 50.378226939239 | | 2005 | 50.41211974982 | | 2004 | 50.443439957274 | | 2003 | 50.473458367377 | | 2002 | 50.503248259133 | | 2001 | 50.533239786043 | | 2000 | 50.557673996169 | | 1999 | 50.575406413199 | | 1998 | 50.585690899146 | | 1997 | 50.590068948573 | | 1996 | 50.592203466305 | | 1995 | 50.592316306361 | | 1994 | 50.591531341922 | | 1993 | 50.593240785153 | | 1992 | 50.597029815728 | | 1991 | 50.599551719415 | | 1990 | 50.601866593608 | | 1989 | 50.603963653303 | | 1988 | 50.603893158554 | | 1987 | 50.597642046202 | | 1986 | 50.585683833562 | | 1985 | 50.572240737181 | | 1984 | 50.555577455804 | | 1983 | 50.533859111559 | | 1982 | 50.508271285355 | | 1981 | 50.479428372893 | | 1980 | 50.446662158197 | | 1979 | 50.407550211047 | | 1978 | 50.362871815158 | | 1977 | 50.316808630649 | | 1976 | 50.272117298483 | | 1975 | 50.230630581557 | | 1974 | 50.191501343683 | | 1973 | 50.154561656033 | | 1972 | 50.12302721603 | | 1971 | 50.096404192365 | | 1970 | 50.076584805963 | | 1969 | 50.065253048931 | | 1968 | 50.060709700047 | | 1967 | 50.061337287337 | | 1966 | 50.06399640101 | | 1965 | 50.068555570111 | | 1964 | 50.074696206608 | | 1963 | 50.082085112521 | | 1962 | 50.088392755289 | | 1961 | 50.094874016594 | | 1960 | 50.101369363911 |
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