[R-meta] I2 or p to choose the effect model

[Viechtbauer, Wolfgang (SP)]

Hi Lorenzo,

I^2 is a relative measure of heterogeneity. Saying 40% (or whatever cutoff) indicates 'great heterogeneity' is therefore not correct. 40% could represent a trivial amount of heterogeneity (in an absolute sense) if the studies are all quite large or it could suggest huge fluctuations in the underlying true effects if the studies are all quite small (or anything in between).

Borenstein discusses this in his books. See also:

Rücker, G., Schwarzer, G., Carpenter, J. R., & Schumacher, M. (2008). Undue reliance on I2 in assessing heterogeneity may mislead. BMC Medical Research Methodology, 8(79). https://doi.org/10.1186/1471-2288-8-79

Also, choosing a model based on the presence/absence of a certain amount of heterogeneity (however quantified) is not really a defensible strategy. It really comes down to the types of inferences you want to make. See here:

https://wviechtb.github.io/metafor/reference/metafor-package.html

Best,
Wolfgang

>-----Original Message-----
>From: R-sig-meta-analysis [mailto:r-sig-meta-analysis-bounces using r-project.org] On
>Behalf Of Martin Lobo
>Sent: Wednesday, 15 September, 2021 15:13
>To: r-sig-meta-analysis using r-project.org; Martin Lobo
>Subject: [R-meta] I2 or p to choose the effect model
>
>Hi Everyone.
>
>I have the following question.
>The Cochraine manual defines an I2 greater than 40% as great heterogeneity, so we
>should choose a random effects model. How should it be interpreted when this I2 is
>accompanied by a p much higher than 0.05?
>
>In this particular case it is a mean difference target.
>I do not know if the interpretation should be different according to the type of
>meta analysis
>
>Thank you
>
>Lorenzo Mart�n Lobo MTSAC, FACC, FESC
>Especialista Jerarquizado en Cardiolog�a
>Jefe de Dpto Enf. Cardiovasculares y Cardiometabolismo Hospital Militar Campo de
>Mayo.
>Jefe de Cardiolog�a Hospital Militar Campo de Mayo
>Ex Jefe de Unidad Coronaria Hospital Militar Campo de Mayo
>Miembro Titular de la Sociedad Argentina de Cardiolog�a
>Fellow American College of Cardiology
>Fellow European Society of Cardiology
>Ex Miembro del Area de Investigaci�n de la SAC
>Ex Director del Consejo de Aterosclerosis y Trombosis de la SAC
>Miembro Asesor del Consejo de Aterosclerosis y Trombosis de la SAC
>Ex Director del Consejo de Epidemiolog�a y Prevenci�n Cardiovascular de la SAC
>
>Miembro Asesor del Consejo de Epidemiolog�a y Prevenci�n Cardiovascular de la SAC
>
>Experto en Lipidos de la Sociedad Argentina de Lipidos.
>Miembro de la Sociedad Argentina de Lipidos.
>Instructor de ACLS de la American Heart Association