Chapter 5 Gaussian Statistics ? An Overview The Gaussian distribution (normal or bell-shaped distribution) is a widely used statistical distribution and it is generally used as the foundation for statistical qual- ity control. Simply measuring the time-zero values of a parameter (resistor values, mechanical tolerances, children heights, class grades on a test, etc.) can result in a distribution of values which can be described by a normal distribution. 5.1 Normal Distribution The normal distribution f(x) shown in Fig. 5.1 is defined by the equation: f (x) = 1 ? ? 2? exp { ? [ x ? x50 ? ? 2 ]2 } . (5.1) +??? x50 Parameter: x f(x) Histogram Parameter : x Fr eq ue nc y