I have a model (attached) which is looking at stability of humour across time, and also looking at whether a best-friend's humour influences your later humour use. The model is based on an APIM approach, hence the parameter constraints (I have indistinguishable dyads). 

  • When I run this with my full sample (N=457) I get a good fit.
  • When I run it with a large subsample, I get good fit (n=356)
  • When I run it with a small subsample (the group that I want to do the analysis on!) I get the following warning "The model is probably unidentified. In order to achieve identifiability, it will probably be necessary to impose 2 additional constraints." 

Normally I can identify where the problem lies when I get that kind of error, but I have never seen it appear as a function of subsample. It doesn't make sense to me that the model can be missing constraints only when a smaller sample is being used. I've tried creating an SPSS file with only the subsample I want instead of selecting them but this gives exactly the same response.

Please also note that I do not get the warning when I delete the two gender variables. However, I need to include these in response to reviewers' comments. The issue seems to be linked to those two variables though because I still get the warning if I delete the age variables instead of the gender variables. 

Thanks in advance :)

Simon

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