Statistical methods for assessing observer variability in clinical measures.

Background Traumatic brain injury (TBI) is the commonest cause of death and disability in UK Citizens aged 1–40. In England three (National Institute of Health and Care Excellence - NICE) guidelines have been implemented to improve TBI outcomes. All guidelines recommended increased CT imaging. The second guideline recommended the management of patients with severe TBI in specialist neuroscience centres. This study uses national data and interrupted time series analysis to assess the impact of the NICE guidelines. Individual level Office of National Statistics (ONS) cause of death data linked to Hospital Episode Statistics for inpatient admissions in England between 1998–2017 were used to estimate the monthly population mortality and admission rate for TBI. An interrupted time series analysis was conducted with intervention points when each guideline was introduced. The analysis was stratified by guideline recommendation specific age groups (0–15, 16–64 and 65+). The monthly TBI mortality and admission rate in the 65+ age group increased from 0.5 to 1.5 and 10 to 30 per 100, 000 population respectively. The increasing mortality rate was unaffected by the introduction any of the guidelines. The introduction of the 2nd NICE Head Injury guideline was associated with a significant reduction in the monthly TBI mortality rate in 16–64 age group (−0.005; 95% CI: −0.002 to −0.007). In the 0–15 age group the TBI mortality rate fell from around 0.05 to 0.01 per 100 000 population, the trend was unaffected by the guidelines. Conclusion The introduction of NICE head injury guidelines was associated with reduced population based mortality rates after specialist care was recommended for severe TBI. The improvement was solely observed in 16–64 year olds. The cause of the observed increased admission and mortality rate in those 65+ and potential treatments for TBI in this age group requires further investigation.