One-sided Bayesian t test with the BayesFactor package - How to get posterior of d?

Comments

• EJ

  February 2017

  Hi Moritz,

  I would apply the two-sided test and then toss out all the negative values for d.

  Cheers,
  E.J.
• duplex_

  February 2017

  Hi EJ,
  thanks, I tried that out. I used

  median d for one-sided test

  median(chains[,4][chains[,4]>0])

  for that. However, in some cases a really unrealistic high value for d is estimated. I attached an example here https://syncandshare.lrz.de/dl/fiBV1uWpk5kvu2xkKdZDUS1o/onesidedBF.rar

  The descriptives are
  Low Mean 3.17 SD 0.54
  Hig hMean 3.19 SD 0.35
  which gives a conventional d of d = 0.03

  Without the negative values, d = 0.17 is estimated, in JASP the value is even d = 0.195
  

  In other cases, the one sided d is closer to the two sided value. I really do not know what to make out of that.
• EJ

  February 2017

  Sure but this makes sense, right? If you look at the mode, it should be near zero. But the median is the 50% cut-off point, so creating a one-sided test makes a big difference. So it is not unrealistically high. It is just that with a non-symmetric distribution, you don't want to summarize with a single point. Looking at the entire distribution is better, imo.
  E.J.
• duplex_

  February 2017

  Want do you think of reporting the one-sided BF and the "two-sided" normal d? (of course, annotating that)
• EJ

  February 2017

  Yes, that is exactly my preferred way of reporting the results!
  E.J.