Danial

Unique metrics published on Facebook reporting surfaces are metrics that count the number of people who took an action, rather than the number of actions taken.

These metrics are considered estimated and sampled, and depend on factors such as how many accounts are used by each person on Facebook Company Products. When a person has more than one account and takes actions (such as liking photos or adding comments) on the separate accounts, these actions may be counted separately even though they were made by the same person.