Is consensus required in story estimation? My answer to this question is yes. In Agile, Planning Poker is estimation and planning technique which is consensus-based. Planning Poker, where the facilitator or the Product Owner reads the User Story or the product backlog items to the team and team estimate it considering the effort it will take to finish it.
The team can estimate the user story or product backlog item and assign a value from the series 1, 2, 3, 5, 8, 13, 20, 40 and 100. This value will become the face value of the user story which will be called Story Points. The team discusses the product backlog item, asking questions to each other and also to the product owners as applicable and needed. At the end of the product backlog item discussion, it’s time for each team member to privately select and assigns a value to the discussed user story or product backlog item. This is usually done by using Planning Poker cards so that each estimator can pick the card and reveal it at the same time.
When the estimates are revealed, if all team members selected the same value then that becomes the estimate of the backlog item. If the estimates are different than the team discusses their estimates and share their views on why they estimate it to be a particular value. Once the discussion is finished, each estimator selects the card and reveal it at the same time.
This process is repeated until consensus is achieved or estimators decide to move to next the product backlog item or User Story.