I was wondering what the adaption to the formula should be in case of multiple groups or longitudinal data (i.e. several time points).
As provided in the related / linked question, source: Hu, L.; Bentler, Peter (1999). "Cutoff criteria for fit indexes in covariance structure analysis: Conventional criteria versus new alternatives". Structural Equation Modeling. 6 (1): 1–55. https://dx.doi.org/10.1080%2F10705519909540118