Johari Window questionnaire and Communication style questionnaire have been combined with the result of final solo presentation. Would this justify the use of Communication competency as a mediator?
You will need to provide more information in order to get a more complete response. As a general statement, communication competency can be considered a mediator between openness and communication performance if it lies on the causal pathway between the two. You can test this using a mediation modelling approach, by determining the amount of the outcome that is explained via the indirect pathway (i.e. via the mediator). Of course, all these methods rely on content expertise for guidance as well as the use of the appropriate mediation model.
I am attaching a paper I recently wrote on mediation analysis. It may provide you with some ideas, as well as an array of models that were tested.
I hope this helps
Ariel
Article Using mediation analysis to identify causal mechanisms in di...
Generally, to say that B is a mediator of the causal relationship between A and C, the model should predict that A causes B and that B causes C. In your case, it might not make sense to say that openness causes communication competency. This means it should not be considered a mediator.
However, communication competency may change the relationship between openness and communication performance. Among people who are high in communication competency, the relationship between openness and communication performance might be strongly positive. Among people who are low in communication competency, this relationship is likely to be weaker, perhaps even negative. In this case, communication competency would be a moderator, not a mediator, of the relationship.
If by openness you mean the willingness to share one's values & beliefs as well as one's ability to perceive another person's communicative intention, than communication competency may moderate. In this condition, an individual's emotional intelligence and empathetic ability would be moderating factors. Considerable research exists on "communicative emotional intelligence" in relationship based interactions..