Mann-Whitney U Test.
The Mann-Whitney U test is a nonparametric alternative to the independent sample t test. It can be used in situations where the assumptions of the t test cannot reasonably be met. Use the data from the previous example (repeated below) to compute the Mann-Whitney U test.
You will find a description (and a link to a procedure for computing the test) here:
Control Group
4, 9, 1, 2, 8, 9, 13, 12, 13, 12, 7, 6
Threat Group
7, 8, 7, 2, 6, 9, 7, 10, 5, 0, 10, 8
As before you can use the U test procedure given in the link above or SPSS. but it would also be a good exercise for you to attempt to "program" the analysis in Excel.