[Numeration of patients from anonymous data: a method established with the epidemiological data of public health of Paris].

Anonymity in the registration of medical information for computerized data, which is imposed by French legislation, complicates the processing and utilization of epidemiological data at Paris's Public Hospitals ("Assistance Publique de Paris"). The number of patients may only be counted by linkage of anonymous data from files containing information on hospital stays. Some characteristics of this procedure are described. An original method for refusing the procedure giving anormalous results, based on probability calculation, is developed and applied to one example.