Chi-squared test KDD Part of Correlation Analysis. χ2=∑i=1n∑j=1m(cij−eij)2eij\chi^{2}=\sum_{i=1}^{n} \sum_{j=1}^{m} \frac{\left(c_{i j}-e_{i j}\right)^{2}}{e_{i j}}χ2=i=1∑nj=1∑meij(cij−eij)2 zero → no Correlation larger value → more Correlation cells with very differenct actual count compared to expected count contribute the most