Identification ability of the first five letters of Christian name and surname

Identifiers must be easy for access and discrimination. Usual identification by surname and christian name is convenient, for these two identifiers are almost always available. Their discrimination ability was studied in terms of the theory of information and the rate of homonymy. In the French language, the first five letters of the surname provide information equal to 12.11 bits and the rate of homonymy is about 0.659%. If one adds the first three letters of the first name, the gain in the quantity of information is 1.68 bits and the rate of homonymy becomes 0.087%. So the first five letters of a surname and the first three letters of a christian name ensure a relatively satisfactory identification and may constitute a significant way of reinforcing the discrimination power of another identification system.