 Solution

ID: past-exam-of-the-probability-statistics-and-options-i-course-of-the-university-of-oxford/2008/o/1/ii/solution

The pooled CC count is

83 + 50 = 133

, the case total is 1939, and the grand total is 3874. Under the null, the common estimated CC proportion is

133/3874

. Multiplication by the fixed case total gives

E_{CC, case} = \frac{1939 \cdot 133}{3874} = 66.5687 \dots \approx 66.6.

This is the fitted expected count, rather than a separate observation.

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