The use of disease severity scores arose first in other specialties primarily as a means of allowing comparison between heterogeneous groups of patients. For example how can you compare the efficiency of two adult orthopaedic units if the length of stay in hospital A is significantly longer than hospital B but the average age of the patients is significantly greater in hospital A? The development of a disease severity score would allow such variation in patient mix to be taken into account and the two units compared fairly with variation in their mix of patients, at baseline, removed. In neonatal care, survival rate was chosen as the most important outcome for comparison and hence most scores were designed to adjust for risk of death particularly in preterm babies.