Spearman's Correlation and effect size I have completed data collection and I have a Spearman's correlation of .64. My advisor is wanting me to report the effect size and from everything I have read and can find it appears that .64 would fall into the large effect size category. However, he is wanting me to square .64 and report that number as the effect size. Why? I am very confused why I would need to square the number.

Squared Pearson correlation is equal to the “proportion of variance in $y$ explained by $x$”. This is also equal to a common regression metric called $R^2$ that has an intimate relationship to minimization of square loss and maximum likelihood estimation when a conditional Gaussian variable is assumed in a generalized linear model (when there is an intercept in the model, which is most of the time).
Your advisor seems to want to mimic that. As Spearman correlation has a similar relationship to proportional odds ordinal logistic regression and Pearson correlation has to regular OLS linear regression, I would not be surprised to hear that there is a relationship to maximum likelihood estimation for the proportional odds model, though I don’t know that.
