How to: One-way ANOVA

One-way ANOVA compares the means of three or more unmatched groups. If your data are matched, learn about repeated measures one-way ANOVA. If you want to perform a nonparametric test, read about the Kruskal-Wallis and Friedman tests.

1. Enter data

You can enter the actual values you want to analyze (raw data) or the mean and SD (or SEM) of each group.

Enter raw data

From the Welcome (or New Table and graph) dialog, choose a vertical scatter plot from the Column tab.

If you aren't ready to enter your own data, choose to use sample data, and choose: One-way ANOVA - Ordinary.

Enter the data for each group into a separate column. The two groups do not have be the same size (it's OK to leave some cells empty). Since the data are unmatched, it makes no sense to enter any row titles.

Enter averaged data

Prism also lets you perform one-way ANOVA with data entered as mean, SD (or SEM), and N. This can be useful if you are entering data from another program or publication.

From the Welcome (or New Table and graph) dialog, choose the Grouped tab. That's right. Even though you want to do one-way ANOVA, you should pick the two-way tab (since the one-way table doesn't allow for entry of mean and SD or SEM). Then choose any graph from the top row, and choose to enter the data as Mean, SD and N or as Mean, SEM and N. Entering N is essential.

Enter the data all on one row. Because there is only one row, the data really only has one grouping variable even though entered on a grouped table.

2. Choose one-way ANOVA

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

3. Choose a post test

How to choose.

4. Review the results and inspect the graph

ANOVA investigates the likelihood that the difference among the means could have been caused by chance. The most important results are the P value and the results of post tests.

Before accepting the results, review the analysis checklist.