• The chi-square statistic (χ2) is a measure of the difference between the observed and expected frequencies of the outcomes of a set of events or variables.

  • Chi-square is useful for analyzing such differences in categorical variables, especially those that are nominal in nature.
  • χ2depends on the size of the difference between actual and observed values, degrees of freedom and sample size.
  • χ2 can be used to test whether two variables are related or independent of each other.
  • It can also be used to check the correspondence between the observed distribution and the theoretical frequency distribution.