1928 12.2 1932 11.9 1936 11.5 1948 11.9 1952 11.5 1956 11.5 1960 11. 1964 11.4 1968 11.08 1972 11.07 1976 11.08 1980 11.06 1984 10.97 1988 10.54 1992 10.82 1996 10.94 2000 10.75 2004 10.93 2008 10.78 2012 10.75