User stories are the primary mechanism for defining intended system behavior in Lean-Agile organizations.1 They are the most granular unit of work typically estimated by teams for planning purposes, and they are most often estimated using story points.
A story point is an arbitrary measure of effort that represents the team’s assessment of how long it will take to implement a story relative to other stories.2 A modified Fibonacci scale – 1, 2, 3, 5, 8, 13, 20, 40 – is often used to rank one story’s level of effort against another. For example, a 1-point story is expected to take half the time for the team to implement as a 2-point story.
Planning Poker is one common technique used by teams to estimating user stories in their backlog.3 In a Planning Poker session, a team discusses each user story and familiarizes themselves with requirements and acceptance criteria. Each estimator then privately selects a card marked with the story point value that they believe represents the appropriate level of effort for the story. The team then reveals all cards at the same time. If there is consensus on a story’s effort, that estimate is assigned to the story. If there is no consensus, further discussion is needed to uncover reasons for differences of opinion. The team votes as many times as needed to achieve consensus.
A team’s velocity is a measurement of the number of story points it can complete in a given interval, and it is the primary capacity measure used to determine whether the team can deliver a specific user story in a particular timeframe. Hence, assigning story points to user stories is a critical prerequisite to accurate planning within both the Program and Team segments.