| Year | Value | | 2022 | 48.284194725191 | | 2021 | 48.256629836115 | | 2020 | 48.230912898297 | | 2019 | 48.207730659654 | | 2018 | 48.185477371429 | | 2017 | 48.163969173275 | | 2016 | 48.142462100405 | | 2015 | 48.121308760265 | | 2014 | 48.099871356707 | | 2013 | 48.077250049793 | | 2012 | 48.053286247584 | | 2011 | 48.027675800611 | | 2010 | 47.984991907649 | | 2009 | 47.925628537243 | | 2008 | 47.865136984877 | | 2007 | 47.803552758034 | | 2006 | 47.740123602498 | | 2005 | 47.674910080525 | | 2004 | 47.606537184328 | | 2003 | 47.532375827932 | | 2002 | 47.456851520881 | | 2001 | 47.386925235071 | | 2000 | 47.318867054377 | | 1999 | 47.246097631824 | | 1998 | 47.170718908519 | | 1997 | 47.096084159443 | | 1996 | 47.015310454741 | | 1995 | 46.92858838437 | | 1994 | 46.839878740131 | | 1993 | 46.746723893886 | | 1992 | 46.649075756265 | | 1991 | 46.556733120878 | | 1990 | 46.476894413732 | | 1989 | 46.40081001966 | | 1988 | 46.320133154817 | | 1987 | 46.235360436158 | | 1986 | 46.146683201706 | | 1985 | 46.053691939906 | | 1984 | 45.957742148853 | | 1983 | 45.859976966409 | | 1982 | 45.760853312067 | | 1981 | 45.706057218224 | | 1980 | 45.714422549901 | | 1979 | 45.732092706278 | | 1978 | 45.74062301335 | | 1977 | 45.753986866792 | | 1976 | 45.778607085736 | | 1975 | 45.804338158381 | | 1974 | 45.824098915199 | | 1973 | 45.844430282092 | | 1972 | 45.86478184118 | | 1971 | 45.895893730258 | | 1970 | 45.94916868527 | | 1969 | 46.014436146611 | | 1968 | 46.089244403897 | | 1967 | 46.170979698711 | | 1966 | 46.267662548736 | | 1965 | 46.375573426444 | | 1964 | 46.49187592319 | | 1963 | 46.614162011457 | | 1962 | 46.744887411149 | | 1961 | 46.89764518038 | | 1960 | 47.043798186207 |
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