Acceptance criteria define conditions that must be met so that the affected Backlog Item is considered fulfilled. These can be refined requirements, special Quality Attributes or Constraints or boundary conditions (QA&C) of the described function, or procedural conditions during implementation.
Estimates lead to good acceptance criteria. Good acceptance criteria lead to better estimates.
During the refinement Acceptance criteria can also be assumptions for the implementation. They are intended to narrow down the goals and results of a Backlog Item for the WorkingTeam, the Product Owner, and the Stakeholders to the point where there is a common understanding of what needs to be accomplished and what needs to be done by the Working Team to accomplish it. This will enable the Working Team to estimate the Backlog Item.
Large differences in the team member’s individual estimates indicate that there are different views and assumptions within the Working Team about the content, outcomes, Acceptance Criteria, and activities needed to achieve them.
Acceptance Criteria vs. Definition-of-done
Often the same Acceptance Criteria are set again and again for the same types of Backlog Items. These Acceptance Criteria should then be created as items in the Definition-of-done for the respective Backlog Item Type, so these do not have to be written on the backlog items again and again. Such, only the specific agreements for each individual Backlog Item are written as Acceptance Criteria on the Backlog Item.