A statistical test that examines whether observed frequencies in categorical data differ significantly from expected frequencies. Commonly used to test independence between variables or goodness of fit.
Named after the Greek letter χ (chi) used to represent the test statistic, squared to ensure positive values. Developed by Karl Pearson in 1900, who chose the Greek letter chi arbitrarily to represent his new test statistic, following mathematical convention of using Greek letters for statistical measures.
Chi-square is perfect for answering 'Is this just coincidence?' questions with categorical data - like whether gender and major choice are related or just random! The test compares what you actually observed versus what you'd expect if there was no relationship, measuring how 'surprised' you should be by your results.
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