The normal probability plot is a graphical technique for normality testing: assessing whether or not a data set is approximately normally distributed. The data are plotted against a theoretical normal distribution in such a way that the points should form an approximate straight line. Departures from this straight line indicate departures from normality.
A Normal Probability Plot is a compares the values in a data set (on the vertical axis) with their associated quantile (probability) values derived from a standardized normal distribution (on the horizontal axis).
- The normal probability plot is a plotting of “Point percentages”
- If we get a straight line, we can say the process is normally distributed.
- Thus, a normal probability plot could be used to determine Process capability.