) is a measure of proportional reduction in error in cross tabulation analysis.
As an example, consider the table below, which describes a fictitious sample of 350 individuals, categorized by relationship status and blood pressure.
Assume that the relationship status is the independent variable, the blood pressure is the dependent variable, i.e., the question asked is "can the blood pressure be predicted better if the relationship status is known?"
Thus, considering the relationship status will not change the prediction that people have a normal blood pressure, even though the data indicate that being married increases the probability of high blood pressure.
If the question is changed, e.g. by asking "What is the predicted relationship status based on blood pressure?,"