An objective metric is one that provides facts, explanations and information that are not subject to personal interpretation or distortion by personal feelings or prejudices. 
For example, average price per unit is an objective measure while perceived value is not.
Objectivity is one of the 10 Characteristics of an Ideal Metric designated by the Marketing Accountability Standards Board.
Quality assured metric
- Accountable Marketing: Linking marketing actions to financial performance, 1st Edition; Eds. Stewart, David W. & Gugel, Craig; Routledge, 2016.
- Universal Marketing Dictionary Project, 2023.