Additional variables - may often add nuance or an external explanation for a relationship. – is a variable that explains how two variables are related in different ways for different people or different situations. – explains why two variables may be related based an explanation that is internal.

1. Moderator

2. Mediator

Explanation:

Moderator has the capability to help assess the relationship strength between two other variables because it is a third party variable. For example if we are considering the strength of relationship between salary and shopping expenditure then this relation will be stronger for women and less strong for men. The reason is that gender is a moderator here which helps assess the relationship strength among two variables better. It is qualitative in nature.

Mediator affects the independant variable which then alters the values of the dependant variable. For example if we are considering the strength of relationship between salary and shopping expenditure then this relation will be disturbed if the residual income is considered here. People with higher salaries or income have higher residual income which they can spent elsewhere hence they can spend more on shoppings. If we remove this middle variable, I mean the Mediator (Residual Income), the relationship picture gets blurred. It is quantitative in nature.