In my mediation model I have only one exogenous and endogenous variable and a mediator. Considering that within the conceptual framework of the work there are other variables but they do not have any relationship with the mediator as such the mediation test did not include them. I therefore wonder if such segregated models can stand. Thank you
Yes, this the correct use of mediation. If you start with data indicating the model IV=>DV is correct, you can add a third variable (M) as a mediator: IV=>M=>DV.
However, it is important that you collect data on all three variables: For each data point you use, you need to measure IV, M, and DV. So if you already have data for the IV and DV, but not M, you need to collect more data and measure all three.
Well.. my research area is physical sciences precisely chemistry, which involves data generation and analysis through mechanical instruments hence not based on statistical analysis evaluation. I therefore wish you all the best my friend.