| Year | Value | | 2021 | 4.3770491803279 | | 2020 | 4.3770491803279 | | 2019 | 4.3770491803279 | | 2018 | 4.3770491803279 | | 2017 | 4.3770491803279 | | 2016 | 4.3770491803279 | | 2015 | 4.3770491803279 | | 2014 | 4.3770491803279 | | 2013 | 4.3770491803279 | | 2012 | 4.3770491803279 | | 2011 | 4.3770491803279 | | 2010 | 4.3770491803279 | | 2009 | 4.3770491803279 | | 2008 | 4.3770491803279 | | 2007 | 4.3770491803279 | | 2006 | 3.7704918032787 | | 2005 | 3.6065573770492 | | 2004 | 3.2786885245902 | | 2003 | 3.2786885245902 | | 2002 | 3.2786885245902 | | 2001 | 3.2786885245902 | | 2000 | 3.2786885245902 | | 1999 | 3.2786885245902 | | 1998 | 3.2786885245902 | | 1997 | 3.1147540983607 | | 1996 | 3.1147540983607 | | 1995 | 3.2786885245902 | | 1994 | 4.0983606557377 | | 1993 | 4.4262295081967 | | 1992 | 4.4262295081967 | | 1991 | 4.5901639344262 | | 1990 | 4.7540983606557 | | 1989 | 4.9180327868852 | | 1988 | 4.9180327868852 | | 1987 | 4.9180327868852 | | 1986 | 5.4098360655738 | | 1985 | 5.4098360655738 | | 1984 | 5.7377049180328 | | 1983 | 6.0655737704918 | | 1982 | 6.5573770491803 | | 1981 | 7.0491803278689 | | 1980 | 7.3770491803279 | | 1979 | 7.7049180327869 | | 1978 | 8.1967213114754 | | 1977 | 8.1967213114754 | | 1976 | 8.1967213114754 | | 1975 | 8.1967213114754 | | 1974 | 8.6885245901639 | | 1973 | 8.1967213114754 | | 1972 | 8.1967213114754 | | 1971 | 8.1967213114754 | | 1970 | 8.1967213114754 | | 1969 | 8.1967213114754 | | 1968 | 8.1967213114754 | | 1967 | 8.1967213114754 | | 1966 | 8.1967213114754 | | 1965 | 8.1967213114754 | | 1964 | 8.1967213114754 | | 1963 | 8.1967213114754 | | 1962 | 8.1967213114754 | | 1961 | 8.1967213114754 |
|