To explore the relationship between case mix index (CMI) and the bed allocation in clinical departments, and to evaluate the performance of bed scale of departments at tertiary hospitals based on CMI.

Based on the HIS system of a tertiary hospital, the authors collected the disease treatment information and bed allocation information of each clinical department in 2015. The CMI value was calculated by means of diagnosis-related group(DRG), while the proportion of cases and average daily beds occupancy corresponding to the quartile of the CMI value of each department was also counted. Then the bed occupancy and distribution of various patients were analyzed.

The hospital′s overall CMI value, DRG groups, DRG cases at the departments, days of stay, DRGs, CMI values and its quartiles were calculated. It was found that the medical and surgical CMIs had a linear relationship with the critical proportion (r=0.998, 0.996, P<0.001). The main influencing factors of average daily bed occupancy were ranged from high to low as followed: the number of cases that were allocated in the group, employee numbers and CMI (F=87.656, P<0.001).

CMI is an ideal indicator for the difficulty of medical services at different departments and for evaluating the bed scale performance. Hence it can be used as an important reference for bed number adjustment in hospitals.

Case mix index; Tertiary hospital; Bed size; Performance evaluation