| Year | Value | | 2021 | 14.130434782609 | | 2020 | 14.130434782609 | | 2019 | 14.130434782609 | | 2018 | 14.140316205534 | | 2017 | 13.636363636364 | | 2016 | 11.594202898551 | | 2015 | 7.2134387351779 | | 2014 | 8.9690382081686 | | 2013 | 8.1719367588933 | | 2012 | 9.2654808959157 | | 2011 | 10.144927536232 | | 2010 | 10.606060606061 | | 2009 | 11.034255599473 | | 2008 | 11.791831357049 | | 2007 | 10.70487483531 | | 2006 | 9.9802371541502 | | 2005 | 10.638998682477 | | 2004 | 10.210803689065 | | 2003 | 9.8814229249012 | | 2002 | 9.8814229249012 | | 2001 | 10.869565217391 | | 2000 | 10.869565217391 | | 1999 | 10.70487483531 | | 1998 | 10.70487483531 | | 1997 | 10.70487483531 | | 1996 | 10.606060606061 | | 1995 | 10.540184453228 | | 1994 | 10.70487483531 | | 1993 | 10.869565217391 | | 1992 | 10.935441370224 | | 1991 | 10.507246376812 | | 1990 | 10.441370223979 | | 1989 | 9.9143610013175 | | 1988 | 11.166007905138 | | 1987 | 10.737812911726 | | 1986 | 9.4532279314888 | | 1985 | 10.013175230566 | | 1984 | 9.7826086956522 | | 1983 | 9.3214756258234 | | 1982 | 9.4861660079051 | | 1981 | 9.8155467720685 | | 1980 | 9.6179183135705 | | 1979 | 10.046113306983 | | 1978 | 9.5191040843215 | | 1977 | 9.4861660079051 | | 1976 | 11.6930171278 | | 1975 | 12.252964426878 | | 1974 | 11.6930171278 | | 1973 | 11.6930171278 | | 1972 | 11.6930171278 | | 1971 | 11.857707509881 | | 1970 | 12.121212121212 | | 1969 | 12.022397891963 | | 1968 | 12.022397891963 | | 1967 | 11.857707509881 | | 1966 | 11.857707509881 | | 1965 | 11.6930171278 | | 1964 | 11.6930171278 | | 1963 | 11.627140974967 | | 1962 | 11.627140974967 | | 1961 | 11.791831357049 |
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