The draft lottery of 1969 was biased. What was the error made by the draft lottery statisticians?
The balls containing birthdays was loaded into a container in month order (January first and December last). The container was not sufficiently agitated, so the dates early in the year were still near the bottom and the dates late in the year at the top. Balls were picked (mostly from the top) so December birthdays were much more likely to be selected than January dates.