MetaP: a program to combine P values

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To test java and how to install it:

If you need more information about this software, or to request a copy running on your local machine, send the author an email:

What does this program do?

MetaP performs a meta-analysis and combines the statistical association signals (P values) from independent studies or study populations, taking account of the impacts of sample sizes and effect directions.

What is the system requirement to run this program?

MetaP is a JAVA applet. It needs your internet browser to be JAVA-enabled - which is usually (if not always) true in today's computer. To test whether java is working in your browser, here is a useful link:

Which combined P value should I choose from the output?

MetaP outputs four different combined P values, using different levels of avilable information:

Conventional Fisher's: only considers P values;

Fisher's trend: considers P values and effect directions;

Stouffer's z: considers P values and sample sizes;

Stouffer's z trend: considers P values, sample sizes, and effect directions.

Geneally speaking you should look at the P value corrected for as many as factors as allowed by your data. That is, if you have both sample size and effect direction information available, the Stouffer's z trend is probably the most accurate one to look at.


Each of the included methods in MetaP has its assumptions and conditions. In addition, each of the combined P values is based on one particular arbitrary distribution. Because of this, it is the author's view that the combined P values generated here may be viewed as ROUGH PREDICTIONS, and can NOT be applied universally. Users are advised to study these methods before the interpretation of the results.


Whitlock, M. C. Combining probability from independent tests: the weighted Z-method is superior to Fisher's approach. J Evol Biol 18, 1368-73 (2005).

For questions and comments, contact the author


This software tool is free for public uses. The author keeps all the copyright. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.