Exact P-Values Upon Request: Breaking with an APA Guideline

The 6th edition of the APA style manual (American Psychological Association, 2010) states the following on the topic of reporting p-values:

“When reporting p values, report exact p values (e.g., p = .031) to two or three decimal places. However, report p values less than .001 as p < .001. The tradition of reporting p values in the form p < .10, p < .05, p < .01, and so forth, was appropriate in a time when only limited tables of critical values were available.”

(p. 114)

These and other recommendations from the APA have always been a guideline for how output in JASP is formatted: many of our tables – often containing p-values – can be copied and pasted directly into your APA-style manuscript. This is one of several features that makes JASP so user-friendly. Figure 1 below shows an example of p-values for three correlation coefficients:

Figure 1. Correlation matrix in JASP

However, JASP also has an open-source nature. This means that anyone can contribute, provide suggestions, and report bugs. Recently, an old discussion was revived with the request to have JASP display exact p-values: some journals require these and JASP did not present them.

So we went to work to enable this feature in JASP. In the upcoming release, JASP version 0.8.2, you will be able to request exact p-values through the Preferences accessible in the top-right hamburger menu

When you enable this option, you will break with the tradition of reporting p-values in the form p < .001, which was arguably appropriate in a time without free, friendly, and flexible statistical software.

Figure 2. Exact p-values in JASP

As Figure 2 shows, selecting “Display exact p-values” in the Preference menu will display the p-values in scientific notation with 4 significant figures, similar to how we represent Bayes factors. Of course, this does not mean that p-values are just as diagnostic as Bayes factors! To read more about the diagnosticity of p-values, please go to our previous blogpost on this topic.

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American Psychological Association. (2009). Publication manual of the American Psychological Association. Washington, D.C.: American Psychological Association.

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About the author

Erik-Jan van Kesteren

Erik Jan van Kesteren is a PhD candidate at Utrecht University. At JASP, he is responsible for adding plots, functions, and UI elements, and interfacing R and C++.