| Year | Value | | 2021 | 10.526315789474 | | 2020 | 10.526315789474 | | 2019 | 10.526315789474 | | 2018 | 10.526315789474 | | 2017 | 10.526315789474 | | 2016 | 10.526315789474 | | 2015 | 10.526315789474 | | 2014 | 10.526315789474 | | 2013 | 10.526315789474 | | 2012 | 10.526315789474 | | 2011 | 10.526315789474 | | 2010 | 10.526315789474 | | 2009 | 10.526315789474 | | 2008 | 10.526315789474 | | 2007 | 10.526315789474 | | 2006 | 10.526315789474 | | 2005 | 10.526315789474 | | 2004 | 10.721247563353 | | 2003 | 11.695906432748 | | 2002 | 11.695906432748 | | 2001 | 11.695906432748 | | 2000 | 13.060428849903 | | 1999 | 13.060428849903 | | 1998 | 12.865497076023 | | 1997 | 13.840155945419 | | 1996 | 14.814814814815 | | 1995 | 14.814814814815 | | 1994 | 15.789473684211 | | 1993 | 15.789473684211 | | 1992 | 15.789473684211 | | 1991 | 15.789473684211 | | 1990 | 15.009746588694 | | 1989 | 14.035087719298 | | 1988 | 14.035087719298 | | 1987 | 13.840155945419 | | 1986 | 13.840155945419 | | 1985 | 13.840155945419 | | 1984 | 14.424951267056 | | 1983 | 14.424951267056 | | 1982 | 17.153996101364 | | 1981 | 18.518518518519 | | 1980 | 19.688109161793 | | 1979 | 20.662768031189 | | 1978 | 20.662768031189 | | 1977 | 20.662768031189 | | 1976 | 20.662768031189 | | 1975 | 20.662768031189 | | 1974 | 21.637426900585 | | 1973 | 21.442495126706 | | 1972 | 19.688109161793 | | 1971 | 19.688109161793 | | 1970 | 19.103313840156 | | 1969 | 19.103313840156 | | 1968 | 19.103313840156 | | 1967 | 19.103313840156 | | 1966 | 19.103313840156 | | 1965 | 19.103313840156 | | 1964 | 19.103313840156 | | 1963 | 19.103313840156 | | 1962 | 18.908382066277 | | 1961 | 18.908382066277 |
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