To quantify differences in hospital costs between socioeconomic groups and the development over time.
Register data on somatic specialised hospital admissions for patients aged between 25 and 84 in Finland in 1998-2010 were used with income data individually linked to them. The cost of an admission was calculated by multiplying the number of a patient's inpatient days by the inpatient day cost of the patient's DRG. We calculated age-standardised admission costs per resident and per user as well as costs per inpatient day and concentration indices separately for men and women.
Hospital admission costs reduced with increasing income. The difference between the extreme income quintiles was more than 50% throughout the study period, and this difference widened. However, the cost per inpatient day was more than 20% higher in the highest income group. The differences between income groups were the most prominent in disease categories involving surgery.
The growth between socioeconomic groups in hospital costs is presumably mainly due to increasing differences in morbidity. More attention needs to be paid to prevention of health inequalities and access to and content of primary care among low-income groups in order to decrease the need for hospitalisations.