Correlation Analysis(Nominal Data) a X(chi-square)test (Observed-Expected) x Expected a The larger the x value the more likely the variables are elated the cells that contribute the most to the x2 value are those whose actual count is very different from the expected count Correlation does not imply causality of hospitals and of car-theft in a city are correlated Both are causally linked to the third variable: population 同济大学软件学院 ool of Software Engineering. Tongpi Unversity 1515 Correlation Analysis (Nominal Data) ◼ Χ2 (chi-square) test ◼ The larger the Χ2 value, the more likely the variables are related ◼ The cells that contribute the most to the Χ2 value are those whose actual count is very different from the expected count ◼ Correlation does not imply causality ◆ # of hospitals and # of car-theft in a city are correlated ◆ Both are causally linked to the third variable: population  − = Expected Observed Expected 2 2 ( ) 