[R-meta] Moderator level getting removed from model

[Viechtbauer Wolfgang (SP)]

Dear Shannon,

Indeed, rma() will omit a coefficient from the model if it is not estimable. What does

table(choiceaccdata$tridiff, choiceaccdata$Provides.Decision.Aids)

show? I suspect this will reveal why this coefficient is not estimable.

So the only thing one could print for that coefficient would be NA (not available). Are you looking for a way to show this?

Best,
Wolfgang

>-----Original Message-----
>From: R-sig-meta-analysis [mailto:r-sig-meta-analysis-bounces at r-
>project.org] On Behalf Of Shannon Duncan
>Sent: Monday, 12 February, 2018 18:23
>To: r-sig-meta-analysis at r-project.org
>Subject: [R-meta] Moderator level getting removed from model
>
>Hello,
>
>I have a question that I can't seem to find an answer to, hoping someone
>here can help me out. We are running the following model:
>
>resalt <- metafor::rma(cohens_d, variance, mods = ~ factor(tridiff) *
>Provides.Decision.Aids, test = "t", data = choiceaccdata)
>
>resalt
>
>## tau^2 (estimated amount of residual heterogeneity):     0.0574 (SE =
>0.0175)
>## tau (square root of estimated tau^2 value):             0.2395
>## I^2 (residual heterogeneity / unaccounted variability): 67.78%
>## H^2 (unaccounted variability / sampling variability):   3.10
>## R^2 (amount of heterogeneity accounted for):            39.40%
>##
>## Test for Residual Heterogeneity:
>## QE(df = 72) = 195.8927, p-val < .0001
>##
>## Test of Moderators (coefficient(s) 2:5):
>## F(df1 = 4, df2 = 72) = 6.8504, p-val < .0001
>##
>## Model Results:
>##
>##                                          estimate      se     tval
>pval
>## intrcpt                                   -0.2234  0.0527  -4.2434
><.0001
>## factor(tridiff)2                          -0.1642  0.1415  -1.1609
>0.2495
>## factor(tridiff)3                          -0.4823  0.1523  -3.1656
>0.0023
>## Provides.Decision.Aids                     0.2183  0.0996   2.1910
>0.0317
>## factor(tridiff)3:Provides.Decision.Aids    0.6595  0.2218   2.9736
>0.0040
>##                                            ci.lb    ci.ub
>## intrcpt                                  -0.3284  -0.1185  ***
>## factor(tridiff)2                         -0.4462   0.1178
>## factor(tridiff)3                         -0.7860  -0.1786   **
>## Provides.Decision.Aids                    0.0197   0.4169    *
>## factor(tridiff)3:Provides.Decision.Aids   0.2174   1.1017   **
>
>As you can see, it's not showing the second level of the factor  tridiff
>(tridiff2) interacting with Decision Aids. I realise this is probably due
>to redundancy or something of that sort, but we would like to see it
>printed out. Is that at all possible?
>
>Thank you for your time and any insight you can provide,
>Shannon