Problem 8. In a retrospective study of the possible effect of blood group on the incidence of peptic ulcers, Woolf (1955) obtained data from three cities. The table gives for each city data for blood groups 0 and A only. In each city, blood group is recorded for peptic ulcer subjects and for a control series of individuals not having peptic ulcer. Peptic Ulcer Control Group 0 Group A Group 0 Group A London 911 579 4578 4219 Manchester 361 246 4532 3775 Newcastle 396 219 6598 5261 a. Compute the odds ratio for each city with a confidence interval. Interpret. b. Suppose that it is required to estimate P(ulcer|A) - P(ulcer|0). What further information is needed to do this from the current data