Individuals in a relationship are (are they getting as much as they are giving).

propinquity filter

attractiveness filter

compatibility filter

balance sheet filter

balance sheet filter

Explanation:

Balance sheet filter falls under the filter theory of mate selection which suggests that people use a filtering mechanism that enable them sort out a potential mate from a "pool of candidates.

Balance sheet filter is a method by which individuals select mates whereby individuals look out for reciprocity. This person looks at what someone can offer that he cannot find in anyone else.