| Year | Value | | 2022 | 52.155237032341 | | 2021 | 51.659691115823 | | 2020 | 51.145712069644 | | 2019 | 50.623788394023 | | 2018 | 50.087054922281 | | 2017 | 49.542073390169 | | 2016 | 48.992523226556 | | 2015 | 48.439072598811 | | 2014 | 47.878240039515 | | 2013 | 47.322306540579 | | 2012 | 46.773910628013 | | 2011 | 46.23362039762 | | 2010 | 45.684283299208 | | 2009 | 45.107182892716 | | 2008 | 44.527353088627 | | 2007 | 43.946304759117 | | 2006 | 43.381183301492 | | 2005 | 42.804148030741 | | 2004 | 42.218118173902 | | 2003 | 41.638393696394 | | 2002 | 41.067564397087 | | 2001 | 40.501705094958 | | 2000 | 39.976680671036 | | 1999 | 39.502155901666 | | 1998 | 39.037282101426 | | 1997 | 38.572543550721 | | 1996 | 38.113941476335 | | 1995 | 37.662397712406 | | 1994 | 37.206093254215 | | 1993 | 36.747629554914 | | 1992 | 36.293239262902 | | 1991 | 35.835660318438 | | 1990 | 35.370146392537 | | 1989 | 34.892789729249 | | 1988 | 34.418444722385 | | 1987 | 33.929136635978 | | 1986 | 33.437617981338 | | 1985 | 32.94109670196 | | 1984 | 32.44281203633 | | 1983 | 31.947024028091 | | 1982 | 31.468679020124 | | 1981 | 30.951536384216 | | 1980 | 30.394534583466 | | 1979 | 29.845344895617 | | 1978 | 29.309507423956 | | 1977 | 28.858435820397 | | 1976 | 28.493342219647 | | 1975 | 28.132281442417 | | 1974 | 27.825244386589 | | 1973 | 27.473213485345 | | 1972 | 27.158557438867 | | 1971 | 26.875148089612 | | 1970 | 26.624977101463 | | 1969 | 26.385047344505 | | 1968 | 26.142528383892 | | 1967 | 25.898494390366 | | 1966 | 25.657919615864 | | 1965 | 25.432326862047 | | 1964 | 25.200762556281 | | 1963 | 24.750240637673 | | 1962 | 24.307476824341 | | 1961 | 23.836914244691 | | 1960 | 23.345877966545 |
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