The justification for this procedure is that the judges are assumed to make decisions by dichotomizing a continuous variable with logistic distributed error (this one statistical justification for logistic regression; see https://en.wikipedia.org/wiki/Logistic_regression#Latent_var...). The mean difference in the continuous variable is given by the log odds ratio times some constant, and the standard deviation of the continuous variable is pi/sqrt(3) times the same constant. Because the logistic distribution resembles a normal distribution (see https://en.wikipedia.org/wiki/Logistic_distribution and figure in paper), the standardized mean difference given by this method will approximately equal the standardized mean difference of the latent continuous variable.
