Economic incentives and diagnostic coding in a public health care system

We analysed the association between economic incentives and diagnostic coding practice in the Norwegian public health care system. Data included 3,180,578 hospital discharges in Norway covering the period 1999–2008. For reimbursement purposes, all discharges are grouped in diagnosis-related groups (DRGs). We examined pairs of DRGs where the addition of one or more specific diagnoses places the patient in a complicated rather than an uncomplicated group, yielding higher reimbursement. The economic incentive was measured as the potential gain in income by coding a patient as complicated, and we analysed the association between this gain and the share of complicated discharges within the DRG pairs. Using multilevel linear regression modelling, we estimated both differences between hospitals for each DRG pair and changes within hospitals for each DRG pair over time. Over the whole period, a one-DRG-point difference in price was associated with an increased share of complicated discharges of 14.2 (95 % confidence interval [CI] 11.2–17.2) percentage points. However, a one-DRG-point change in prices between years was only associated with a 0.4 (95 % CI (-1.1) to 1.8) percentage point change of discharges into the most complicated diagnostic category. Although there was a strong increase in complicated discharges over time, this was not as closely related to price changes as expected.