A cancer laboratory is estimating the rate of tumorigenesis in two strains of mice, A and B.They have tumor count data for 10 mice in strain A and 13 mice in strain B. Type A mice have been well studied, and information from other laboratories suggests that type A mice have tumor counts that are approximately Poisson-distributed with a mean of 12. Tumor count rates for type B mice are unknown, but type B mice are related to type A mice. The observed tumor counts for the two populations are \begin{array}{c} y_{A}=(12,9,12,14,13,13,15,8,15,6) \\ y_{B}=(11,11,10,9,9,8,7,10,6,8,8,9,7) \end{array}

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