Why is the total number of cases in Tipperary greater than the sum of cases in Tipperary North and Tipperary South for some years?

Most of our data for Tipperary hasn't been geocoded to each of the ridings. Our policy is thus to assign to the North Riding those cases that are registered in the Mid-Western Health Board, and to the South riding those that are registered in the South-Eastern Health Board

Occasionally there are cases where the health board is not given. Such cases cannot be matched to either of the ridings. As a result the rates for "Tipperary (Total)" are generated from the cases assigned to the North Riding, the cases assigned to the South Riding, and those cases which could not be assigned to either riding. It is these unassigned cases which account for the difference.