[R-meta] [netmeta] Error message in network meta-analysis: "Problem with multi-arm studies: Studies with inconsistent treatment estimates"

[Rogasch, Rebecca Manuela Madeleine]

Dear experts,

I'm seeking advice regarding an error message in network meta-analysis using the netmeta package.

To briefly outline the objective and describe the data structure:
I am conducting a network meta-analysis on the effectiveness of PTSD intervention programs.
The primary outcome is the PTSD total symptom score (=continuous outcome).
All studies are randomized-controlled trials. There are 8 three-arm studies in my data set and 64 two-arm studies.
I calculated the SMD (post-post) from means and SDs.

Here is an example for the data structure:


 studlab sampleID  OutcID   TR1   TR2    Mt2TR1  SDt2TR1  Mt2TR2  SDt2TR2  n_TR1 n_TR2 n_total    smd    se

       1      101 10101     EMDR   WL    22.87    20.27    54.21   16.26    15    14      29    -1.65  0.19

     100    10001 1000101   NET    WL    55.07    27.01    76.86   17.14    19    19      38    -0.94  0.12

     104    10401 1040101   NET   PsEd   19.10    11.70    21.20    9.40    17    12      29    -0.19  0.14



When applying the netmeta function I get the following error message:

> mn1 <- netmeta(smd, se, TR1, TR2, studlab, data=dat3, sm="SMD", comb.random=TRUE)

Error: Problems in multi-arm studies!
- Studies with inconsistent treatment estimates: '107', '121', '130', '15', '22', '34', '36', '87'
- Please check original data used as input to netmeta().
- For more details, re-run netmeta() with argument details.chkmultiarm = TRUE.
- Argument 'tol.multiarm' in netmeta() can be used to relax consistency
assumption for multi-arm studies (if appropriate).

My questions are as follows:

  1.  I am not able to make sense of the error message regarding inconsistency within the 3-arm-studies. Can anyone help?
  2.  When setting the argument tol.multiarm = 0.05 it runs without any error message.

However, I am not sure what the argument does, exactly, and haven't been able to find any detailed information.

Does anyone know what the argument does or where I can find further information?

Looking forward to hearing from you!
Best regards,
Rebecca

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