| Year | Value | | 2022 | 0.46249176947456 | | 2021 | 0.39767042381845 | | 2020 | 0.44152432578899 | | 2019 | 0.43008121853313 | | 2018 | 0.37249163791137 | | 2017 | 0.38385024504951 | | 2016 | 0.44049651252337 | | 2015 | 0.40596793128706 | | 2014 | 0.42465642836874 | | 2013 | 0.47127259316765 | | 2012 | 0.4758707308867 | | 2011 | 0.45961944772301 | | 2010 | 0.44138260438983 | | 2009 | 0.39532607351187 | | 2008 | 0.4682311029144 | | 2007 | 0.39845660146699 | | 2006 | 0.43182946456192 | | 2005 | 0.38391365673546 | | 2004 | 0.47941608905692 | | 2003 | 0.81565534252526 | | 2002 | 0.76224502605429 | | 2001 | 1.0520629291887 | | 2000 | 0.91840163471875 | | 1999 | 0.67560075986606 | | 1998 | 0.72083985099418 | | 1997 | 0.74281794332224 | | 1996 | 0.89571741353924 | | 1995 | 1.0804273736464 | | 1994 | 1.1785345993652 | | 1993 | 1.2670601713489 | | 1992 | 1.4726203751385 | | 1991 | 1.2684372641499 | | 1990 | 1.728011562816 | | 1989 | 1.8028516299552 | | 1988 | 1.869076997211 | | 1987 | 1.750710006719 | | 1986 | 1.6674979953403 | | 1985 | 2.0073704359649 | | 1984 | 2.1908492867174 | | 1983 | 2.0359340987193 | | 1982 | 2.0257186775874 | | 1981 | 1.8894491043007 | | 1980 | 1.3168515369191 | | 1979 | 1.3066782558308 | | 1978 | 1.1811218186311 | | 1977 | 1.3721375786881 | | 1976 | 1.2713902824548 | | 1975 | 1.2314865606144 | | 1974 | 0.89830776530128 | | 1973 | 0.91075390184097 | | 1972 | 1.14198705748 | | 1971 | 1.1185006045949 | | 1970 | 1.6964285714286 | | 1969 | 1.0259997668182 | | 1968 | 1.2666873641726 | | 1967 | 1.457146049838 | | 1966 | 1.373454874716 | | 1965 | 1.3955904851844 | | 1964 | 1.0038342531867 | | 1963 | 1.1730075113639 | | 1962 | 1.0453078110693 | | 1961 | 1.122221065483 | | 1960 | 1.1579222339135 |
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