raphaelvallat
Implementing Cohen's Dz for paired sample T-Test
Hallo Raphael, first of - thanks for providing this great library.
I was wondering if you could implement the Cohen's Dz for paired samples. There are already some (closed) issues that your calculation of Cohen's D differs from other packages or from R and that you have good reasons to use the formula you are using. But since Cohen's Dz is simply calculated by
T/sqrt(N) or X_diff.mean() / X_diff.std()
and is also the one often reported (at least in my field) and also the one you find when looking for effect sized on Wikipedia, I would really appreciate it.
Best Vincent
Hi Vincent,
Thanks for opening the issue. While it is straightforward to add the Cohen Dz to the low-level compute_effsize function, there's some work in making that new metric available in higher-level functions such as pairwise_tests.
I think we would need to expose a new keyword-argument to all impacted functions, e.g.
pairwise_test(..., paired_cohen_type="avg")
pairwise_test(..., paired_cohen_type="dz")
Alternatively, we could define this as a global option.
Curious to hear what you and other thinks here.
Best Raphael
Hey Raphael,
... there's some work in making that new metric available in higher-level functions ...
yeah that makes sense. I don't have a good overview of your project nor am I a good coder, so I don't wanna make assumptions about the best solution. However, it seems counterintuitive to me to have a paired_cohen_type argument, when a user chooses a different effect size, e.g., Hedge's g ...
Generally, to me it seems that Cohen's Dz is better known than Cohen's D_avg and I would go for dz as the standard.
In the end it's your choice.
Best, Vincent
Would it be okay to just add something like cohen_z to the low-level compute_effsize? Then users could pass that into the effsize argument in pairwise_test and related functions, so both Cohen's are available (separately) and other effect sizes as well. Maybe if there is concern about users requesting inappropriate effect sizes given a certain stat, a warning could be raised.
