The bias correction is estimated as:

$$\Delta_{c}=\Delta_{obs}\frac{\Gamma\left(\frac{n_{control}-1}{2}\right)}{\Gamma\left(\frac{n_{control}-1}{2}\right)\Gamma\left(\frac{n_{control}-2}{2}\right)}$$

where \(\Delta\) is the observed effect size, \(\Delta_{c}\) is the corrected estimate of \(\Delta\), and \(n_{control}\) is the control-group sample size.