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χ2 Statistic

Definition

The χ2 statistic, also known as chi-square statistic, measures how well observed data fits expected data according to a certain hypothesis. It is commonly used in tests involving categorical variables.

Analogy

Think of a puzzle where you have to fit different-shaped pieces into their respective spaces. The χ2 statistic tells you how well your pieces fit together compared to what was expected. If your puzzle pieces match closely with expectations, then your χ2 value will be small; otherwise, if they don't fit well, your χ2 value will be larger.

Related terms

Degrees of Freedom: Represents the number of categories minus one for which values can vary freely after certain restrictions are imposed on them.

P-value: A probability associated with the χ2 statistic that indicates whether observed differences between expected and observed data are statistically significant.

Contingency Table: A table that displays the frequency or count of observations falling into different categories for two categorical variables. It is often used in χ2 tests.