Normal probability plot


h = normplot(X)


h = normplot(X) displays a normal probability plot of the data in X. For matrix X, normplot displays a line for each column of X. h is a handle to the plotted lines.

The plot has the sample data displayed with the plot symbol '+'. Superimposed on the plot is a line joining the first and third quartiles of each column of X (a robust linear fit of the sample order statistics.) This line is extrapolated out to the ends of the sample to help evaluate the linearity of the data.

The purpose of a normal probability plot is to graphically assess whether the data in X could come from a normal distribution. If the data are normal the plot will be linear. Other distribution types will introduce curvature in the plot. normplot uses midpoint probability plotting positions. Use probplot when the data included censored observations.


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Generate a Normal Probability Plot

Generate random sample data from a normal distribution with mu = 10 and sigma = 1.

rng default;  % For reproducibility
x = normrnd(10,1,25,1);

Create a normal probability plot of the sample data.


The plot indicates that the data follows a normal distribution.

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