Efficacy of empirical data in Emotional Wellness (mental health) occurs when constants are measured and changed and legitimacy of the data occurs when it is generated by the client. The constant in Emotional Wellness (mental health) is the clients’ emotional state. Measuring, tacking and improving this constant at every session is what brings about the efficacy of an intervention.
Evidence-based is a term coaches and mental health professionals use to indicate someone did a study on the process they are using. This does not mean these practitioners produce measurable outcomes. This is an important distinction if you need an indication of the competence and performance of a practitioner.