A parity bit is a simple mechanism for detecting errors in data transmitted over an unreliable connection such as a telephone line. The basic idea is that an additional bit is transmitted after each group of 8 bits so that a single bit error in the transmission can be detected. Parity bits can be computed for either even parity or odd parity. If even parity is selected then the parity bit that is transmitted is chosen so that the total number of one bits transmitted (8 bits of data plus the parity bit) is even. When odd parity is selected the parity bit is chosen so that the total number of one bits transmitted is odd.