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area numbers 700 through 728 were assigned to railroad workers until 1963, at which time the practice was discontinued. The area number has little meaning today due to the mobility of people. The next two-digit group, called the group number, has no special significance except to break the numbers into convenient blocks. The last four-digit group, called the serial number, is assigned sequentially within each group. Note that no group contains only zeroes.

In a study done at Duke University, examining the SSNs of approximately 150,000 individuals, the last six digits of the SSNs were uniformly distributed. This uniform distribution is particularly valuable for certain hash-code indexing techniques.

In the 1960s, the use of the SSN spread to the Internal Revenue Service for tax purposes, the Department of Defense for military designation, and the Civil Service Commission for employee identification. In 1976, states were authorized to use the SSN for tax purposes, public assistance, and for driver's license or motor vehicle registration. A number of states use the SSN on the driver's license.

Analysis and Forecast

Value of a Universal Citizen Identifier

Simply put, the most reliable method of integrating data from multiple sources is to have a unique identification number known to all sources. In the absence of such a number, combining data from multiple sources or even reliably identifying a person within a single source is difficult. If we fail to identify a person in the health care environment, that person's data are split into multiple records and valuable data are misplaced.

Community health care information networks (CHINs) and statewide alliances are becoming popular in which health care information about a person is available, with proper safeguards, to those people responsible for a patient's care. Failure to associate known health care data about a patient can lead to serious consequences. For example, if the patient is allergic to a certain drug and he or she is misidentified and that information is not available, that important point could be missed. If, in fact, we believe that information about the patient's health, medications, allergies, problems, and treatment plans is important, then we must be sure that the information is available to the proper health care providers. The highest probability of making that happen is through the use of a unique universal identifier.

Requirements for a Universal Citizen Identifier

The universal citizen identifier (UCI) must be unique. Each person must possess one and only one identification number. A UCI number, once assigned, can never be reassigned. A UCI should be assigned at birth or when a person becomes a resident of this country.

The UCI should be context free. The UCI is a pointer to data about a person. It should not attempt to convey any information about gender, age, or geographical area where a patient was born or now lives. Its sole purpose is to link the number to one or more data banks.

A system must be established for creating an identification number for foreign visitors and illegal aliens. Such a number must also possess the characteristic of uniqueness and must never be reassigned. We now have international telephone numbers that use a country code. These numbers are of various lengths and format. We might use a similar scheme for personal identifiers. The popularity of international travel and the availability of the Internet make it particularly feasible to transmit a person's health record to any country. A known identification number would make that process more reliable.

One of the commonest errors that results in the misidentification of a patient, even with the use of a patient identification number, is the transposition of two numbers. The use of a check digit would provide a solution. There are several check digit algorithms. Generally the check digit is generated by multiplying each digit of the identifier, in order, by a weighted multiplier. The resulting product is divided by some number and the remainder is taken as the check digit. This digit becomes part of the identification number and is entered into the

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