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stixbox >> stixbox > Graphics > normplot

normplot

Normal probability plot

Calling Sequence

normplot(x)
normplot(x, symbol)

Parameters

x :

a n-by-m matrix of doubles, the data

symbol :

a string or a 1-by-m vector string, the symbol to plot (default="+")

Description

In this graphics, the data is plotted on x-axis and quantiles of the normal distribution are plotted on y-axis. A straight red line is plotted based on the first and third quantiles of the data.

Interpretation

If the data is close to the normal distribution, then the points are close to a straight line. If the points are far away from the straight line, then the data is likely have a non-normal distribution.

Compatibility

This function is partially compatible with Matlab's normplot. More precisely, the "h" output argument of Matlab is not available in Stixbox's normplot. This feature does not seem necessary, since the current handle can be get with "h=gcf()", as for any graphics. Furthermore, Matlab's normplot Y-axis is named "Probability", with unequal ticks corresponding to the normal quantiles : this Y-axis is associated with unequal spaces between the ticks, which makes the plot weird. Stixbox's normplot has the same Y-axis as presented in Wikipedia : this Y-axis is associated with equal spaces between the ticks.

Examples

x=distfun_normrnd(0,1,50,1);
scf();
normplot(x)
// Change the symbol
clf();
normplot(x,"b.")

// See with uniform distribution
x=distfun_unifrnd(0,1,50,1);
clf();
normplot(x);

// See with chi-square distribution
x=distfun_chi2rnd(2,50,1);
clf();
normplot(x);

See also

Authors

Bibliography

https://en.wikipedia.org/wiki/Normal_probability_plot

http://fr.mathworks.com/help/stats/normplot.html


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