One of the advantages for employees in a group health plan is the contribution most employers make toward the cost of the health coverage premium â in many cases, employers pay one-half or more of the monthly premium for an employee.
The basic format consists of five decimal numerical digits. An extended ZIP+4 code, introduced in 1983, includes the five digits of the ZIP code, a hyphen, and four additional digits that determine a more specific location within a given ZIP code. The USPS provides a free online lookup tool for ZIP codes.
The researchers at Carnegie Mellon set out to see if they could discover people's numbers by first exploiting what is publicly known about how the numbers are derived. The Social Security number's first three digits -- called the area number -- is issued according to the Zip code of the mailing address provided in the application form. The fourth and fifth digits -- known as the group number -- transition slowly, and often remain constant over several years for a given region.