Historical Values

The best way to calculate velocity is with historical values, if they are available. Teams monitor how many story points they complete each sprint and calculate an average based on previous sprints. The Mean Value Theorem suggests that across numerous sprints, the average number of story points will approach the true average for the team. There will be high values and low values for any team, but after several sprints, the team should have a solid idea of about how many story points they typically complete.

Teams often improve their velocity over time, but it usually grows in a gradual slope. Rarely will a team drastically improve their velocity in a short time frame. Significant variations in completed story points from previous sprints may be due to other influences. If a holiday falls within a sprint, team members may not work that day, and reduce the amount of completed work. When measuring historical values, the Scrum team must be aware of outside influences that may have created outlier data points.

The problem with estimating velocity based on historical values is that no team begins with historical values, and it takes a series of sprints to build up the data. A new team on an existing project has no history of working together. An existing team assigned to a new project has no knowledge of the product. As teams evolve, their velocity will change. While historical values are the most accurate way to estimate velocity, it also takes several sprints to get the values to use. Because of this, historical values are often better used to hone velocity over time.

Recommended Further Reading

The following materials may assist you in order to get the most out of this course: