| Year | Value | | 2022 | 50.65539829176 | | 2021 | 50.655048945662 | | 2020 | 50.661698995362 | | 2019 | 50.673761078127 | | 2018 | 50.69091298092 | | 2017 | 50.711600275962 | | 2016 | 50.735986754582 | | 2015 | 50.761781437116 | | 2014 | 50.791194165535 | | 2013 | 50.826085974799 | | 2012 | 50.860264103786 | | 2011 | 50.895854943854 | | 2010 | 50.943628106727 | | 2009 | 51.018595989049 | | 2008 | 51.111548882958 | | 2007 | 51.215212166547 | | 2006 | 51.323064056694 | | 2005 | 51.428593663396 | | 2004 | 51.523099667145 | | 2003 | 51.606365876719 | | 2002 | 51.686353655503 | | 2001 | 51.770031762279 | | 2000 | 51.848078926425 | | 1999 | 51.892511130065 | | 1998 | 51.913143122968 | | 1997 | 51.923092083394 | | 1996 | 51.922378507617 | | 1995 | 51.899722885469 | | 1994 | 51.86751199167 | | 1993 | 51.82727622584 | | 1992 | 51.77918632824 | | 1991 | 51.731230107458 | | 1990 | 51.685216527215 | | 1989 | 51.639780945166 | | 1988 | 51.598249323961 | | 1987 | 51.563912709817 | | 1986 | 51.544115651693 | | 1985 | 51.530386308188 | | 1984 | 51.507998061674 | | 1983 | 51.491177176537 | | 1982 | 51.494380557751 | | 1981 | 51.494680525465 | | 1980 | 51.466863201734 | | 1979 | 51.419727009926 | | 1978 | 51.363117435227 | | 1977 | 51.300863777523 | | 1976 | 51.23478445065 | | 1975 | 51.165313290811 | | 1974 | 51.091283886242 | | 1973 | 51.011059059517 | | 1972 | 50.923394540741 | | 1971 | 50.828185700691 | | 1970 | 50.726433675077 | | 1969 | 50.655985912022 | | 1968 | 50.631283392398 | | 1967 | 50.617232052594 | | 1966 | 50.602089112895 | | 1965 | 50.585644052636 | | 1964 | 50.566365696389 | | 1963 | 50.546441797049 | | 1962 | 50.527843698688 | | 1961 | 50.508673683805 | | 1960 | 50.488903421458 |
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