Specification limits are set by the customers; often, Voice of the Customer is referred to as the customer specification limits.
Z scores are the number of standard deviations a score or a value (x) away from the mean and are a measure of the dispersion of data.
The normal probability plot is a graphical technique for normality testing. Used to assess data set follows normal distribution.
Poisson distribution is a discrete probability distribution; it describes the mean number of events occurring in a fixed time interval.
The chi square (χ2) distribution is the best method to test a population variance against a known or assumed value of the population variance