The two ways to describe how a mediator differs from a moderator
are:
Mediator is always the middle
variable between the Independent Variable and the Dependent
Variable. The main objective of the mediator is to define the
relationship between the IV and DV. With the introduction of
mediator IV indirectly influences the DV through the mediator. For
example- Exercising (IV) is positively influencing physical fitness
(mediator) that promotes healthy diet (DV). When the effect of
mediator variable physical fitness is removed, the effect between
the exercise and healthy diet disappear.
Mediator never act as a third party
variable that influences the strength of relationship between the
IV and DV as the moderate does. Moderator always measure the
strength of relationship between IV and DV.