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Output_tssem2.txt [6] | 3.43 KB |
Hello everyone,
I am currently conducting TSSEM using correlation matrices from primary mediation studies. I ran into some problems during the process and hoped that someone could help me.
1) I understand that in studies which reported standardized path coefficients, only the a-path can be treated as a correlation and that the b- and c-paths need to be computed with the impliedR()function (see also here: https://openmx.ssri.psu.edu/node/4671). For me, this is the case in one study - however, there is a missing value (a-path) for which I am not sure what to insert into the Amatrix. I tried “NA” which gives me the following error report: “Fehler in strsplit(freePara1, "*", fixed = TRUE) : nicht-character Argument”. When I use zero, the outcome matrix provides me with the same values I already have retrieved from the primary study. I could not find a guideline on how to include missing values into impliedR() and hoped someone might have an idea.
2) tssem1() returned with an OpenMx status of 5 or sometimes 6 at first. I read in another thread (https://openmx.ssri.psu.edu/node/4244) that a solution might be fixing small heterogeneity variances to 0 for tssem1(), which I tried:
RE <- Diag(c(0,0,"0.01*Tau2_3_3"))
RE
; (although all variances were very small: Tau2_1_1 and Tau2_2_2: 0.0000000001, Tau2_3_3: 0.0203500436) and after that, the OpenMx status was 0. Running tssem2() also works, however the fit indices from tssem2() do not seem to make sense (see attached output) and I do not get standard errors or p-values. Is it a possibility that I just do not have enough studies to pool (four studies investigating five mediators) and too many missings?
pattern.na(matrix.list2, show.na = TRUE, type=c("tssem"))
X M Y
X 4 4 0
M 4 0 1
Y 0 1 1
3) How exactly can I include the sample size of a study investigating more than one mediator into the TSSEM? As I need to report a sample size in the n vector for each correlation matrix, I currently split the sample size of the study with two mediators in order not to overrepresent it by putting in the whole sample size two times. Is that correct?
Any help would be greatly appreciated.
Thanks a lot in advance,
Hannah