Other uses of normal probability plots

In addition to the use of normal probability plots previously mentioned, i.e. to assess significant effects from screening experiments, and to check residuals after fitting models, there are some other useful applications which are briefly discussed in this section. 

Estimates of mean and standard deviation directly firom the plot 

Normally distributed data form a straight line in the plot. The intersection of this line with the horizontal line P(y) = 50 %, gives the abscisse coordinate which corresponds to the mean. 

On commercially normal probability graph paper there are printed lines which will intersect the probability distribution line at o, 2 7 and 3(7. An estimate of the standard deviation can therefore be obtained directly from the plot. 

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