| Year | Value | | 2022 | 50.428756676963 | | 2021 | 50.401542603822 | | 2020 | 50.386307983641 | | 2019 | 50.358836126649 | | 2018 | 50.322214837938 | | 2017 | 50.293305750269 | | 2016 | 50.270922283308 | | 2015 | 50.240256605208 | | 2014 | 50.196895961991 | | 2013 | 50.148068749065 | | 2012 | 50.09649672808 | | 2011 | 50.046480948583 | | 2010 | 49.987834516184 | | 2009 | 49.9076041528 | | 2008 | 49.775711701361 | | 2007 | 49.631205081725 | | 2006 | 49.49860312604 | | 2005 | 49.37437598727 | | 2004 | 49.281308108363 | | 2003 | 49.196544878221 | | 2002 | 49.116775356485 | | 2001 | 49.052258363385 | | 2000 | 49.004053436908 | | 1999 | 48.967485450495 | | 1998 | 48.932174129039 | | 1997 | 48.894004784986 | | 1996 | 48.864091944745 | | 1995 | 48.83836978964 | | 1994 | 48.814269089265 | | 1993 | 48.797174703651 | | 1992 | 48.77985409137 | | 1991 | 48.771785799698 | | 1990 | 48.779725465003 | | 1989 | 48.790130089256 | | 1988 | 48.791405585454 | | 1987 | 48.785422538878 | | 1986 | 48.779280872856 | | 1985 | 48.771828297387 | | 1984 | 48.765950830048 | | 1983 | 48.767964071758 | | 1982 | 48.772680395002 | | 1981 | 48.770948853063 | | 1980 | 48.755826970324 | | 1979 | 48.72700642455 | | 1978 | 48.690571077355 | | 1977 | 48.651150708285 | | 1976 | 48.603649014246 | | 1975 | 48.55124029213 | | 1974 | 48.534321257937 | | 1973 | 48.550004021375 | | 1972 | 48.565285113402 | | 1971 | 48.368830185425 | | 1970 | 48.182710692302 | | 1969 | 48.200392221235 | | 1968 | 48.195286767295 | | 1967 | 48.187367714874 | | 1966 | 48.179122568775 | | 1965 | 48.173670775835 | | 1964 | 48.166525215165 | | 1963 | 48.157138017373 | | 1962 | 48.143463032321 | | 1961 | 48.121733826504 | | 1960 | 48.097477303402 |
|