Abstract: A medical data analysis service is provided. The service may be implemented as an on-line service using a data analysis server. The data analysis server may maintain patient databases and a community database. Each patient database may be populated with patient medical expense data such as medical bills from health care providers and insurance statements from insurance providers. The service analyzes the data in the databases to identify potential errors. The system detects errors in billing and insurance coverage and enables the patient to query medical expense data. The system enables patient's notes relating to these services to be easily tracked, queried and shared. The system enables a patient to derive additional knowledge from the medical expense and insurance coverage data. This knowledge can be queried by the patient. The system enables a patient to derive more knowledge from collective patient medical expense and insurance coverage data and annotations.