Solution

ID: past-exam-of-the-probability-statistics-and-options-i-course-of-the-university-of-oxford/2010/o/3/a/solution

Under the independence log-linear model for a two-way contingency table, the six cell probabilities factor as
The row distribution has one free parameter and the column distribution two, giving three free parameters under . Under the unrestricted alternative, six cell probabilities sum to one, giving five free parameters under . The difference is two, which is the degrees of freedom of the resulting chi-squared test.

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