Saturday, June 7, 2014

Intro to Normal Probability Plot

Normal Probability Plot:

Normal probability plot is a graphical technique for 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.

The normal probability plot is formed by:
•        Vertical axis: Ordered response values
•        Horizontal axis: Normal order statistic medians

The normal probability plot is used to answer the following questions
•        Are the data normally distributed?

•        What is the nature of the departure from normality (data skewed, shorter than expected tails, longer than expected tails)?


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