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

[Viechtbauer, Wolfgang (SP)]

Dear Marianne,

I suspect that you did not receive any responses, since what you are describing are really unusual cases which have not been discussed in the literature (as far as I know).

I think you will just have to make a decision yourself how to handle these cases and be transparent about how you handled them.

Best,
Wolfgang

>-----Original Message-----
>From: R-sig-meta-analysis [mailto:r-sig-meta-analysis-bounces using r-project.org] On
>Behalf Of Marianne DEBUE
>Sent: Thursday, 21 January, 2021 15:57
>To: r-sig-meta-analysis using 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