Chi-square test for independence

[vicki]

Hi, can somebody explain the Chi-square test for independence please, and how to calculate the Chi-square statistic. Thanks!

[Adrian]

The chi-square test for independence tests the null hypothesis that the row classification factor and the column classification factor are independent. It compares observed and expected frequencies (counts). The expected frequencies are calculated by assuming the null hypothesis is true. The chi-square test statistic is basically the sum of the squares of the differences between the observed and expected frequencies, with each squared difference divided by the corresponding expected frequency.

A large chi-square statistic indicates that somewhere in the table, the observed frequencies differ markedly from the expected frequencies.