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jschipper
use of chi square
You mean a chi-squared distribution? It's widespread use in almost anything relating to hypothesis testing (e.g. confidence intervals, statistical inference, et al).
It is widely used in inference and hypothesis testing to analyse associations. In categorical factors. Like is a factor like smoking (maybe in a non-smoking control group, a 1 pack a day group and a 2 pack a day group) associated with some outcome like increases in number of deaths from lung cancer or associated with more aggressive forms of lung cancer? You would use a chi square procedure to construct a confidence interval or run a hypothesis test or whatever to determine whether or not cigarette smoking is associated with bad outcomes.