How to: Unpaired t test from raw data

This page explains how to enter and analyze raw data. Look elsewhere if you want to enter averaged data, if you want to perform the nonparametric Mann-Whitney test, or if your data are matched so you want to do a paired t test.

1. Create data table and enter data

From the Welcome (or New Table and graph) dialog, choose the Column tab, and then choose a scatter plot with a line at the mean.

If you are not ready to enter your own data, choose sample data and choose: t test - unpaired.

Enter the data for each group into a separate column. The two groups do not have to have the same number of values, and it's OK to leave some cells empty.

Stop. If you want to compare three or more groups, don't use t tests repeatedly. Instead, use one-way ANOVA followed by multiple comparison post tests.

2. Choose the unpaired t test

1.	From the data table, click on the toolbar.

2.	Choose t tests from the list of column analyses.

On the t test dialog, choose the unpaired t test. Choose the Welch's correction if you don't want to assume the two sets of data are sampled from populations with equal variances, and you are willing to accept the loss of power that comes with that choice. That choice is used rarely, so don't check it unless you are quite sure.

4.	Choose a one- or two-tail P value. If in doubt, choose a two-tail P value

3. Review the results

The t test investigates the likelihood that the difference between the means of the two groups could have been caused by chance. So the most important results are the 95% confidence interval for that difference and the P value.

Learn more about interpreting and graphing the results.

Before accepting the results, review the analysis checklist.