[R-meta] Testing interaction term of categorical moderators in rma.mv

[Viechtbauer, Wolfgang (SP)]

Correct. But in this case, you will see that the p-value for the coefficient you are testing is identical to what you get from anova(r1, btt=4). So there is no need to do this, since you already have the test for the interaction.

Best,
Wolfgang

-----Original Message-----
From: Ju Lee [mailto:juhyung2 using stanford.edu] 
Sent: Tuesday, 17 September, 2019 18:05
To: Viechtbauer, Wolfgang (SP); r-sig-meta-analysis using r-project.org
Subject: Re: Testing interaction term of categorical moderators in rma.mv

Dear Wolfgang,

I have to throw in another quick question related to your response. I apologize for this inconvenience.
Now I understood that "btt" argument should basically cover whatever number of coefficients shown in the output. So in case there is only one coefficient for interaction term ( in case of 2 moderators with 2 levels each, so 2x2), I will just need to specify "btt=4:4" as I have done below?

> r1<-rma.mv(hedged,VCV, mods=~ factor(Region) * factor(Consumer.habitat.specialization), method="ML", random = ~ region.chs | Study, data=MHF, struct="DIAG", subset=(!is.na(region.chs)))
> r1

Multivariate Meta-Analysis Model (k = 716; method: ML)

Variance Components: 

outer factor: Study      (nlvls = 160)
inner factor: region.chs (nlvls = 4)

            estim    sqrt  k.lvl  fixed                     level
tau^2.1    0.7810  0.8837    470     no  High latitude:Generalist
tau^2.2    1.0199  1.0099    133     no  High latitude:Specialist
tau^2.3    0.9985  0.9992     90     no   Low latitude:Generalist
tau^2.4    0.3626  0.6022     23     no   Low latitude:Specialist

Test for Residual Heterogeneity: 
QE(df = 712) = 3194.7722, p-val < .0001

Test of Moderators (coefficient(s) 2:4): 
QM(df = 3) = 19.9822, p-val = 0.0002

Model Results:
                                                                              estimate      se     zval    pval    ci.lb
intrcpt                                                                         0.7745  0.0905   8.5554  <.0001   0.5971
factor(Region)Low latitude                                                     -0.5404  0.2551  -2.1179  0.0342  -1.0405
factor(Consumer.habitat.specialization)Specialist                              -0.6569  0.2044  -3.2135  0.0013  -1.0575
factor(Region)Low latitude:factor(Consumer.habitat.specialization)Specialist    0.3572  0.3959   0.9022  0.3670  -0.4188
                                                                                ci.ub     
intrcpt                                                                        0.9519  ***
factor(Region)Low latitude                                                    -0.0403    *
factor(Consumer.habitat.specialization)Specialist                             -0.2562   **
factor(Region)Low latitude:factor(Consumer.habitat.specialization)Specialist   1.1332     

---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1 

> anova(r1,btt=4)

Test of Moderators (coefficient(s) 4): 
QM(df = 1) = 0.8139, p-val = 0.3670

Thank you very much for your help!
Best regards,
JU