A mediator variable is assumed to cause the effect in the outcome variable, and not vice versa. Such as in psychology, a mediator variable would explain how an external environments events is affecting an internal psychological significance.
While a moderator variable is assumed to either reduce or enhance the influence of the independent variable. Such as the effect of loud noise during an exam, on the end exam scores.
Baron & Kenny (1986) highlighted the importance of not using the terms moderator and mediator interchangeably.
Baron & Kenny (1986) wrote:
“The moderator function of third variables, which partitions a focal independent variable into subgroups that establish its domains of maximal effectiveness in regard to a given dependent variable. The mediator function of a third variable, which represents the generative mechanism through which the focal independent variable is able to influence the dependent variable of interest.”
Moderating Variable- moderator is a variable which will cancel the relationship with two variables. Moderator is a variable which will refuse the degree of relationship between two variables. Moderator can be totally canceled the relationship between two variables.
Moderating - changing
Eg: You feel sleep in the class after having a heavy lunch. So there is a relationship. But assume you don’t feel sleep in the class after having a huge lunch. The answer is the moderator, may be the interesting nature of the lecturer or exam fear.
Intervening variable alternatively called mediating variable
Intervening variable – Assume training and job performance, the relationship is positive. Greater the job training better the job performance. How does the training increase the job performance? If you have an answer, then the answer is the intervening variable. Learning is the acquisition of new knowledge and attitude. So training will result in learning which will result in job performance.
For more details please refer the articles given below.
References
Frazier, P.A., Tix, A.P. and Barron, K.E., 2004. Testing moderator and mediator effects in counseling psychology research. Journal of counseling psychology, 51(1), p.115.
Baron, R.M. and Kenny, D.A., 1986. The moderator–mediator variable distinction in social psychological research: Conceptual, strategic, and statistical considerations. Journal of personality and social psychology, 51(6), p.1173.