Mathematics
Chi-Square Tests: Goodness of Fit and Independence
Quick fact
The chi-square statistic is computed by summing (observed - expected)² / expected across all categories. Its distribution is defined by degrees of freedom, and it can be used for both goodness-of-fit and tests of independence.
Why this is interesting
Have you ever wondered if your favorite cereal brand really has more marshmallows than the others? Chi-square tests can tell you if such differences are just random or actually meaningful.