Correction for d (classical t-tests)

[EJWagenmakers]

From the forum -- we could look into this and when we like it we could offer it as an option or provide it in addition to the current d: "I know your focus is more on the Bayesian analyses, but a brief comment on the classic t-tests: The Cohen's d reported in the output table for (classic) paired t-tests seems to be uncorrected for the correlation between observations. This can lead to overestimation of the effect size according to some authors (e.g., [1] ) Perhaps it would be good to mention that the d value is uncorrected? [1] alternative formulae for example in Dunlap, W. P., Cortina, J. M., Vaslow, J. B., & Burke, M. J. (1996). Meta-analysis of experiments with matched groups or repeated measures designs. Psychological Methods, 1(2), 170."

[FransMeerhoff]

Hi @quentingronau

Can you take a look at this one, or give a comment on it?

Cheers Frans

[hcp4715]

I recently encountered this issue and posted my question in the forum: https://forum.cogsci.nl/discussion/3013/what-denominator-does-the-cohens-d-use-on-jasp

Assume that we calculate Cohen's d as suggested here, i.e., use effsize::cohen.d(.., paired=T, ...) to calculate Cohens'd and MBESS::ci.smd() to calculate the Confidence intervals, the Cohens' d is not corrected for the correlation between the pair of data, neither the confidence intervals.

[boutinb]

@JohnnyDoorn Can you have a look to this issue?

[JohnnyDoorn]

Yes, I commented on the issue - where I list how we calculate cohen's d for paired samples, and how we use MBESS to get the confidence interval. It would be nice to have include more types of effect sizes here - just like we did for the 2-sample t-test.

[tomtomme]

Same request of providing more effect size options for RM ANOVA post hoc tests here: https://github.com/jasp-stats/jasp-issues/issues/1915