Document Lpy2QEeED8Dqe3v1vNVLZayN7

Ichool of Public Health Arbor, Michigan 48104 THE UNIVERSITY OF MICHIGAN Department of Biostatistics Area code 313, 764-5450 February 5, 1975 Mr. M. Gerald Ott Biostatistician, Corporate Medical Dept. The Dow Chemical Company Bennett Building 2030 Dow Center Midland, Michigan 48640 Dear Gerry: I've tried to find a reference to the fact that the distribution of the sum of independent Poisson random variables conditional upon a fixed sum is a multinomial. So far I have only found it for the special case of two variables, although the proof given can be easily extended to more variables. The reference is Bross, I.D.J., "Confidence Interval for a Percentage Increase," Biometrics 10, 245 ff. The result we are interested in is on page 249. I enjoyed your visit and I appreciate the opportunity to work with you. Sincerely yours Richard G. Cornell Professor and Chairman R&S 031060 RGC:tlb