Key Concepts

• • χ² distribution is the sum of k squared standard normal variables
• • Mean = k, Variance = 2k, right-skewed (becomes more normal as k increases)
• • Red tail = rejection region: if χ²_stat > χ²_crit, reject H₀
• • Used for goodness-of-fit tests and tests of independence in contingency tables
• • IB Biology: χ² test for association, df = (rows−1)(cols−1)