How To Add Significance Lines To Graphs In GraphPad Prism

In this tutorial I will explain how to use GraphPad Prism to add lines with text to depict statistical significance between datasets on graphs.

What are significance lines?

I don’t believe the correct term is significance lines; but I am going to use this hereafter.

I’m talking about the horizontal, and sometimes zig-zag, lines that are added onto graphs to indicate when significant differences are present between datasets. These lines usually have a symbol (eg *) or text (eg P<0.05) to provide additional information to the reader.

Lline with symbol to show significant differences between datasets in  GraphPad Prism
The significance line and symbol can be used to show that the two datasets are significantly different from one another.

How to add significance lines and symbols to graphs in Prism

Adding significance lines and symbols is incredibly easy in Prism! Simply follow the steps below.

With the graph open in Prism, click on the draw tool at the top. There are a plethora of options available; however, the ones that concern us are the ‘lines with text‘ options.

GraphPad Prism draw tool
The lines with text option can be found at the bottom of the draw tool’s dropdown menu.

Select the option that suits your intention. For example, a horizontal line can be added to show the difference between multiple datasets. Or, use the zig-zag options when there are numerous datasets at different heights on the same graph.

Then, simply click and drag on the graph where you want the line to be. Prism will also ask what symbol to use above the line. You can either select from the options in the list or manually enter your own.

It is then possible to fine-tune the location and adjust either end of the line independently. Also, the snap feature will ensure the lines and symbols are directly above the dataset.

If you want to change the appearance of the line, such as the colour and thickness, then double-click on the line to open up the line settings.

GraphPad Prism format line options
You can change the appearance of the line by double-clicking on it to open up the settings.

How to add symbols without lines to graphs in Prism

If you just want to add a symbol onto the graph, instead of the accompying horizontal line, then simply use the text tool.

By using the text tool you can then enter any text or symbol you desire, such as *.

GraphPad Prism version used: 8.1.2


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