Medical insurance claims as a source of data for research: accuracy of diagnostic coding.

Validation of diagnostic codes in a sample of Hawaii medical insurance claims in 1986 to 1987 revealed 96% accuracy in hospital claims, high enough to supply data for research purposes. In physician claims the accuracy was only 62%. Initiation of two feedback loops to physicians from the insurer in 1989 resulted in a marked improvement of diagnostic coding accuracy by 1992 to 1994.