ACCURACY OF ICD-9-CM CODES IN-HOSPITAL MORBIDITY DATA, VICTORIA - IMPLICATIONS FOR PUBLIC-HEALTH RESEARCH

Hospital morbidity data in the form of International classification of diseases, 9th revision, clinical modification codes are often used fo r epidemiological studies and disease surveillance. We aimed to evalua te the reliability of the Victorian In-patient Minimum Database for us e in epidemiological studies and disease surveillance. Data from 1993- 94 were collected, as part of a coding audit of public hospitals in Vi ctoria, from 7052 randomly selected records. The frequency of discrepa ncy in any coding field was 53 per cent, and of discrepancy in the pri ncipal diagnosis, 22 per cent. New Australian national diagnosis-relat ed group (ANDRG) codes were assigned as a result of discrepancy in 13. 6 per cent of cases. Discrepancy rates increased with increasing rarit y of ANDRG, from 50 per cent to 56 per cent. Predictors of change in A NDRG assignment were discrepancy in the principal diagnosis, ANDRG fre quency of over 0.6 per cent, more than three diagnoses, medical ANDRGs , length of stay over five days and rural hospitals. Rates of any disc repancy increased from 36 per cent in patients with one diagnosis to 9 4 per cent in patients with 12 diagnoses. The discrepancy rates were c onsistent with those of other studies. Coding discrepancy is likely to be caused by universal difficulties associated with the coding of hos pital records, rather than any unique local problems. The predictors o f discrepancy suggest that more complex cases are more prone to coding discrepancy. In areas where the database is less reliable, use of a s upplementary data source, such as linkage studies, would improve relia bility.