[R-meta] Overlapping CIs with significant difference among subgroups

[Viechtbauer, Wolfgang (SP)]

Dear Rafael,

What specifically do you mean by "this practice"? Presenting estimated (average) effects with their CIs when subgrouping the studies based on some categorical variable? Indeed, one cannot directly infer based on the CIs whether the subgroups are actually different from each other. For this, one should conduct a proper test of subgroup differences. One can also directly test whether the difference between two effects is significant or not or present an estimate of the difference between two effects with a corresponding CI (and if that CI excludes 0, then one knows that the test of the difference is significant at alpha = (100 - CI level)/100). But I see nothing generally wrong with the practice of presenting subgroup effects with CIs. 

Best,
Wolfgang

>-----Original Message-----
>From: Rafael Rios [mailto:biorafaelrm using gmail.com]
>Sent: Wednesday, 03 June, 2020 5:27
>To: Viechtbauer, Wolfgang (SP)
>Cc: r-sig-meta-analysis using r-project.org
>Subject: Re: Overlapping CIs with significant difference among subgroups
>
>Dear Dr. Wolfgang,
>
>Thank you very much! Since confidence intervals are not very informative to
>exhibit diferences between subgroups, why is this practice so common among
>meta-analysts? Why not to present standard errors instead of CIs?
>
>Best wishes,
>
>Rafael.
>
>Em ter, 2 de jun de 2020 às 03:48, Viechtbauer, Wolfgang (SP)
><wolfgang.viechtbauer using maastrichtuniversity.nl> escreveu:
>Dear Rafael,
>
>CIs can overlap and yet the difference between the two levels can be
>significant. See, for example:
>
>https://towardsdatascience.com/why-overlapping-confidence-intervals-mean-
>nothing-about-statistical-significance-48360559900a?gi=b673a691634d
>
>https://www.psychologicalscience.org/observer/understanding-confidence-
>intervals-cis-and-effect-size-estimation
>
>https://blog.minitab.com/blog/real-world-quality-improvement/common-
>statistical-mistakes-you-should-avoid
>
>and many more (just google for "test difference overlapping confidence
>intervals" or something along those lines). They don't talk about meta-
>analysis per se, but it's the same principle.
>
>So, you can trust the test of the difference between the levels of the
>moderators.
>
>Best,
>Wolfgang
>
>>-----Original Message-----
>>From: Rafael Rios [mailto:biorafaelrm using gmail.com]
>>Sent: Monday, 01 June, 2020 21:54
>>To: r-sig-meta-analysis using r-project.org; Viechtbauer, Wolfgang (SP)
>>Subject: Overlapping CIs with significant difference among subgroups
>>
>>ATTACHMENT(S) REMOVED: dataset.csv | pruned_super-tree.tre | script.R
>>
>>Dear Wolfgang and All,
>>
>>I conducted a multilevel mixed-effects meta-analysis and found differences
>>between levels of two moderators. I was expecting to find non-overlapped
>>confidence intervals. However, I obtained overlapped confidence intervals
>>for all subgroups. How can I interpret these results? In such situation,
>>should I trust in the Q-test or in the CIs? I controlled for phylogenetic
>>non-independence. Is there a chance of this approach affect the estimation
>>of CIs using predict function? My dataset and script are attached.
>>
>>Best wishes,
>>_______________________________________________________
>>
>>Prof. Dr. Rafael Rios Moura
>>Coordenador de Pesquisa e do NEPEE/CNPq
>>Laboratório de Ecologia e Zoologia (LEZ)
>>UEMG - Unidade Ituiutaba
>>
>>ORCID: http://orcid.org/0000-0002-7911-4734
>>Currículo Lattes: http://lattes.cnpq.br/4264357546465157
>>Research Gate: https://www.researchgate.net/profile/Rafael_Rios_Moura2
>>Rios de Ciência: https://www.youtube.com/channel/UCu2186wIJKji22ai8tvlUfg
>--
>_______________________________________________________