GraphPad Curve Fitting Guide

Plotting t, z, F or chi-square distributions

Plotting t, z, F or chi-square distributions

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Plotting t, z, F or chi-square distributions

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GraphPad Prism can generate probability distributions. This demonstrates Prism's ability to plot functions from user-defined functions, and also the use of hooking info constants to analyses.

Download this Prism file to generate and plot the graphs shown below.

In each case, the simulation generates two (or three) data sets. The first (A) data set plots the entire curve. The equation is written so the second curve (data set B) only plots values where X is less than a specified cutoff value, and the third curve (data set B) only plots values when X is greater than the cutoff value. The second and third data set are plotted with area fill to shade the tails of the distributions. Remove data set B or C from the graph if you only want to shade one tail. For example, here is the equation used for the first graph (z distribution):

G=exp(-0.5*X^2)/sqrt(2*3.1415926)

<A>Y=G

<B>Y=IF(X<-z, G, 0)

<C>Y=IF(X>z, G, 0)

Change the numbers of degrees of freedom and the cutoff values (for shading) in the Info sheet. This demonstrates how values entered into an info sheet can be 'hooked' to constants used in analyses.