Normal probability plot

Normal probability plots are made of raw data, residuals from model fits, and estimated parameters.

The theoretical quantiles are generally chosen to approximate either the mean or the median of the corresponding order statistics.

If the data are consistent with a sample from a normal distribution, the points should lie close to a straight line.

With fewer points, it becomes harder to distinguish between random variability and a substantive deviation from normality.

This article incorporates public domain material from the National Institute of Standards and Technology