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How is a pp plot different from a qq plot?


Asked by Eric Duarte on Dec 09, 2021 FAQ



PP Plots The PP plot for comparing a sample to a theoretical model plots the theoretical proportion less than or equal to each observed value against the actual proportion. For a theoretical cumulative distribution function (F) this means plotting
Thereof,
The quantile-quantile (q-q) plot is a graphical technique for determining if two data sets come from populations with a common distribution . A q-q plot is a plot of the quantiles of the first data set against the quantiles of the second data set.
In this manner, A normal probability plot, or more specifically a quantile-quantile (Q-Q) plot, shows the distribution of the data against the expected normal distribution . For normally distributed data, observations should lie approximately on a straight line. If the data is non-normal, the points form a curve that deviates markedly from a straight line.
Subsequently,
Residuals should be normally distributed and the Q-Q Plot will show this. If residuals follow close to a straight line on this plot, it is a good indication they are normally distributed. An example from the University of Virginia (http://data.library.virginia.edu/diagnostic-plots/) shows a good and bad case.
In addition,
surfc (X,Y,Z) creates a three-dimensional surface plot with a contour plot underneath. A surface plot is a three-dimensional surface that has solid edge colors and solid face colors. The function plots the values in matrix Z as heights above a grid in the x - y plane defined by X and Y.