Normal Probability Plot

Normal probability plot
Normal probability plot

Photo by chansr

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.


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