However the data was not found to be robust at a small area level and there were concerns around overlap with the premature death rate, as cancer is the leading cause of death in Wales.
Fodd bynnag, gwelwyd nad oedd y data'n gadarn ar lefel ardaloedd bach ac roedd pryderon ynglŷn â gorgyffwrdd â'r gyfradd marwolaethau cynamserol, gan mai canser yw'r prif achos marwolaeth yng Nghymru.