# Bayes effect size delta

Hi there,

Two questions about the effect size used in JASP:

- What is an effect size (delta)? Is it Glass's delta?
- How do you convert Cohen's d into delta? (this is straightforward if delta is Glass's delta)

Cheers,

Hannah

PS. Thank you Team JASP - the program is fantastic!!

## Comments

Hi Hannah,

I assume you are talking about the t-test. Delta is the population version of the sample Cohen's d. So it is just the mean population difference divided by the population sd. You can find a detailed description in http://www.ejwagenmakers.com/2016/LyEtAl2016JMP.pdf (and also in the PBR t-test paper by Rouder et al., which is cited in the Ly paper).

Cheers,

E.J.

Very helpful - thank you! And thanks for your speedy reply! Much appreciated:)