Comparing two head injury treatments by linear logistic model.

A linear logistic model is used to compare the performance of a series of head injured patients treated in Auckland with a series obtained from the International Data Bank (IDB), on head injured patients. The IDB patients were treated along conventional lines of neurosurgical management. The Auckland patients were submitted to a regime of elective artificial ventilation of the lungs and heavy sedation, directed against diffuse brain swelling. Two types of comparison were used. First, a model was constructed from the Auckland data of the relationship of outcome to factors relating to the severity of the head injury. This input-output relationship was used to predict the distributions of outcome in the IDB series. Secondly, a descriptive model on the combined Auckland and IDB data was given the option of selecting a dummy variable to indicate whether the source of the patient, Auckland or IDB, had significantly influenced outcome for a given set of other determinants. Differences between Auckland and IDB were only significant if the severity of the head injury in the IDB cases was represented by the set of scores indicating their best condition over the first 24 hours of coma. The scores indicating the condition of the Auckland patients might be comparable to either the 24 hour best or the 24 hour worst IDB scores. One cannot say whether any differences in input-output relationships between the two series arise from differences in coding the input data or from real differences in outcome for given sets of determinants of outcome.