Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2019/ii/paper-4/13j/b/solution

Model 2 is obtained from model 3 by setting . Model 3 is contained in model 1 by choosing the symmetric block parameters
Hence
Assuming every college-pair cell is observed and the models are identifiable, model 1 has parameters and model 3 has . The likelihood-ratio test statistic for model 3 against model 1 is
Under model 3 and the regularity conditions of Wilks theorem,

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