Normal probability plot
h = normplot(X)
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.
This example shows how to generate a normal probability plot using sample data.
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.