Counting the cost of hospitalised injury using administrative data in Australia: three considerations from a retrospective cohort data linkage study.

objectivesTo examine the relative differences in injury hospitalisation cost estimates from hospital administrative data when using (1) hospital reimbursement based on National Efficient Price (NEP) versus local hospital costings methods, (2) inflation factors based on Consumer Price Index (CPI) versus health group index and (3) different healthcare funder's perspectives.

designRetrospective population-based cohort study of linked Queensland Hospital Admitted Patient Data Collection dataset and National Hospital Cost Data Collection data.

settingAll admitted injury-related care episodes occurring within a major trauma hospital in Queensland during 1 January 2012 to 31 December 2017. OUTCOME MEASURE: Total in-patient hospitalisation cost associated with an episode of care.

resultsInjury without catastrophic/severe complications or comorbidities was the most frequently occurring Australian Refined Diagnosis-Related Groups (AR-DRG) over the 6-year period, while rehabilitation with catastrophic complications or comorbidities was the most expensive ($37 938, 95% CI $36 067 to $39 809). Among the top 10 AR-DRGs, seven had NEP-based cost estimates substantially higher than the hospital-reported costs, with differences varying between 2.6% and 43.0%. CPI-inflated costs were significantly lower than health group index-inflated estimates, with observed differences between 7.7% (95% CI 6.9% to 8.7%) and 11.9% (95% CI 10.8% to 13.1%) for the same AR-DRG. Finally, cost estimates were significantly higher for care funded by private health insurers compared with care funded by either the public insurer or compulsory third-party injury insurers, with differences varying significantly between 8.4% (95% CI 7.2% to 30.1%) and 55.0% (95% CI 53.3% to 56.9%) for the same AR-DRG. Care funded by compulsory third-party injury insurers, however, incurred the highest cost for the most expensive AR-DRGs.

conclusionThere were considerable discrepancies in cost estimates for common injury-related hospitalisations depending on type of costing method used, inflation metrics applied and healthcare funder's perspective adopted. These factors need to be considered when evaluating hospital cost in Australia's health system using administrative data.