significance scripts calculate the t-test statistic
for a two-sample difference of means test and shade
the grid cells that are significant at a chosen level. There
are two different forms of the test: one in which we assume the
population variances are equal, and one in
we assume the population variances are unequal.
You can determine which form of the test to use by conducting
a F-test that compares the variances of the two samples. Step-by-step
instructions for running the scripts are listed below.
In the graphic to the
right (click on the map for a larger-size version), we show the
results of a t-test for for DJF for FOAM GCM data, comparing model-predicted
surface temperatures from 6K B.P. to current surface temperatures.
The areas that are shaded gray are signficant at the 99% level.