Replicates and error bars on Grouped graphs

Setting up data tables for entry of replicates or error values

When you create a Grouped table, choices on the Welcome or New Table dialog let you specify side-by-side subcolumns for entry of replicates, or subcolumns for entry of error values computed elsewhere. Learn more about Grouped tables.

The example below is set for entry of three replicate values (triplicates), but you can choose any number from 2 to 52.

The last two choices (grand mean and median) only appear if you choose a grouped column scatter graph.

This next example is set up to enter mean, SD and N for each bar.

"%CV" is the coefficient of variation, which is equals 100SD/Mean. If you enter the %CV, Prism will plot SD error bars.

If you enter N along with the SD, SEM or %CV, you will be able to plot the SD, SEM, or 95% CI (via choices on the Format Graph dialog). If you omit N, Prism can only plot the error value you entered.

Changing the subcolumn format

To plot the replicates or error bars differently, you don't have to remake a graph. Instead, click the Change graph type button.

Use the Format Data Table dialog to specify how you will enter the replicates or error values. If you change from entry of mean and SD to entry mean and SEM, only the labels change (not the numbers). This lets you correct a mistake (if you were actually entering SEM values but mistakenly set up the table with a subcolumn labeled for SD values). Don't make changes in the Format Data Table dialog, when you want to change the way the error bars are plotted. Read on to see how to change error bar plotting.

Choosing how the replicates or error bars are plotted

When you create a new table and enter replicates, you choose not only how the subcolumns are formatted, but also how Prism plots them. You can choose to plot individual replicates, mean only, mean with error bar (which you can specify). Choose all this right under the spot where you choose the number of replicates.

If you choose to enter error values directly, Prism will plot the values you entered (except that when you enter %CV, Prism plots the SD). If you entered Mean, SD (or SEM) and N, you can choose (on the graph) to plot the error bars as SD, SEM or 95% CI.

Changing how replicates or error bars are plotted

To plot the replicates or error bars differently, you don't have to remake a graph. Instead, click the Change graph type button.

The changes you make on the Change Type of Graph dialog apply to all data sets on the graph.

An alternative approach is to double-click anywhere on the graph to bring up the Format Graph dialog. Then click the "All' button so changes you make apply to all data sets. If you don't do this, you might accidentally end up with some data sets having one kind of error bar and other data sets with a different kind of error plotting.