Confirmatory Factor Analysis : validity for a just-identified model I have developed a 3-item questionnaire, and I would like to test the validity of this questionnaire. I wanted to test the validity using confirmatory factor analysis, but since my model is just-identified (DF = 0), all fit measures (RMSEA, Chi-sq, test of close fit, CFI) do not make sense any more.
Can I still test the validity of my questionnaire? How else can I test the validity of my questionnaire?
An example of my model is as below:

Many thanks!

You can add a constraint (equality of factor loadings) and test a τ-equivalent model:
This recent paper proposes this "new" approach:
Czerwiński, S. K., & Atroszko, P. A. (2021). A solution for factorial validity testing of three-item scales: An example of tau-equivalent strict measurement invariance of three-item loneliness scale. Current Psychology. https://doi.org/10.1007/s12144-021-01554-5
