Effects of service delivery versus changes in incidence on trends in injury: A demonstration using hospitalised traumatic brain injury

The relative decline in minor to serious TBI is likely to be related to a change in the probability of admission rather than a change in the population TBI incidence. As most TBI hospitalisations are minor this suggests the trend in TBI hospitalisations was significantly influenced by factors other than changes in population incidence. Any analysis of routinely collected secondary injury data needs to consider case selection carefully, especially if trends are being examined. Applying a severity threshold should give more reliable trends.