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Hi Mike,
many thanks for the fantastic metaSEM package! I used it to combine models from two original studies.
(1) What astonishes me is that some of the structural parameters estimates from TSSEM Stage 2 are even larger than the ones from the individual studies (e.g. study 1: beta = -.40; study two: beta = -.53; TSSEM2: beta = -.66). Naively I had expected that the comnbined TSSEM2 etimates should be somewhere between the ones of the original studies. I am wondering how this is possible. Can I trust this finding?
(2) Since my model contains two mediation paths: Is it possible to get LB confidence intervals for indirect effects?
Many thanks
Johannes
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Hi Johannes,
Thanks.
(1) I don't have a definite answer here. Were the beta = -.40 and beta = -.53 obtained from the over-identified models, e.g., CFA and SEM? If yes, the average of them can be different from TSSEM. The values beta = -.40 and beta = -.53 are based on the assumption that the fitted models are correct. If they are not correct, the average between -.40 and -.53 is missleadig. It is usually difficult to defend that the proposed model fits well in all studies.
The TSSEM takes other assumptions. If you used the fixed-effects TSSEM, the first stage assumes that the correlation matrices are homogeneous, whereas the stage 2 analysis assumes that the proposed model is correct. Personally, I find it more reasonable to use the TSSEM approach.
(2) Yes, please see the examples in Becker92 and Hunter83.
Cheers,
Mike