[R-meta] effect size calculation with a null standard deviation

-----Original Message-----
From: R-sig-meta-analysis [mailto:r-sig-meta-analysis-bounces at r-project.org] On
Behalf Of Marianne DEBUE
Sent: Thursday, 21 January, 2021 15:57
To: r-sig-meta-analysis at r-project.org
Subject: [R-meta] effect size calculation with a null standard deviation

Hi everyone,

I'm conducting a meta-analysis in ecology. I'm using Morris "dpcc1" formulas ( [
https://journals.sagepub.com/doi/10.1177/1094428106291059 |
https://journals.sagepub.com/doi/10.1177/1094428106291059 ] ) to calculate the
effect size and its variance.

The effect size calculation implies a difference between post- and pre-Mean which
is then divided by the pre-Standard deviation.
I was wondering how to deal with studies which have pre-Standard deviation = 0
(leading to a division by 0) ?
How to deal with studies which have pre-Mean = post-Mean and a pre-Standard
deviation = 0 (leading to 0 divided by 0) ? If pre-Mean = post-Mean , can we
consider that the effect size is null, whatever the pre-Standard deviation ?

The variance calculation implies a division by (N - 3) (N : sample size).
How to deal with studies which have N = 3 ( leading to a division by 0) ?

Thank you for your help,

Marianne