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Bayesian Paired Samples t test effect size

How is the effect size in the Bayesian paired sample t test calculated? The "median" effect size in the Bayesian inferential plot is not the same as the Cohen's d (which here is the mean diff/SD of the difference scores, ie the dz) calculated from the frequentist paired samples t test in JASP.

Thanks in advance.



  • Hi Joe,

    population effect size delta = population mu / population sd.

    So it's the population equivalent of Cohen's d (which is a summary based on the sample, not an inference)



  • Thanks EJ. Much appreciated. Is there a reference you can point me to that would help me wrap my head around it better?


  • There's a 2009 paper in Psychonomic Bulletin & Review by Rouder & Morey:


     AUTHOR =    {Rouder, J. N. and Speckman, P. L. and Sun, D. and Morey, R. D. and Iverson, G.},

     TITLE =    {{B}ayesian $t$ Tests for Accepting and Rejecting the Null Hypothesis},

     JOURNAL =   {Psychonomic Bulletin \& Review},

     YEAR =     {2009},

     volume =    {16},

     pages =    {225--237},


  • Awesome. Thanks! Very helpful. I owe you a beer.


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