Chi-Square Goodness of Fit

Tests whether observed categorical frequencies match expected frequencies from a hypothesized distribution.

Formula

χ² = Σ (Oᵢ − Eᵢ)² / Eᵢ, df = categories − 1 − parameters_estimated

Example

Compare observed counts to uniform expected counts and compute χ² to obtain a p-value.

FAQs

Small expected counts?
Combine categories or use exact methods.

When invalid?
Expected frequencies should generally be ≥ 5 for each cell.