What would an expected frequency of zero suggest in a Chi Square test?

An expected frequency of zero in a Chi Square test indicates that, based on the null hypothesis, there are no anticipated observations in that particular category. This situation can occur when the theoretical model used to generate the expected frequencies predicts that a specific outcome should not occur at all, leading to an expectation of zero observations.

In the context of a Chi Square test, it's essential to understand that the expected frequencies are calculated from the data and the null hypothesis; they reflect what we would expect to see if the null hypothesis were true. An observed frequency of zero, while meaningful, can create issues for the Chi Square test, as it can affect the validity of the test results. Understanding the rate of occurrence for each category allows researchers to analyze how their actual data corresponds with the theoretical expectations laid out by the null hypothesis.