Understanding Story Points in Agile Development

In Agile development, story points are a unit of measure used to express estimates of the effort required to fully implement a product backlog item or any other piece of work. This article delves into the concept of story points, how they are assigned, and factors to consider when estimating with story points.

What Are Story Points?

When estimating with story points, each item is assigned a point value, with the raw values themselves being unimportant. What matters are the relative values. For example, a story assigned two points should be twice as much effort as a story assigned one point. It’s the ratios that matter, not the actual numbers.

Factors Influencing Story Point Estimates

Story points represent the effort to develop a story, and thus, the estimate must encompass everything that can affect the effort. This includes:

• Amount of Work: More work typically requires more effort. However, there are economies of scale to consider.
• Complexity: Complex work requires more thinking, trial and error, and may take longer to validate and correct mistakes.
• Risk and Uncertainty: Uncertainty in requirements or technical risks can impact effort. For example, dealing with old, brittle code without automated tests increases the risk and effort.

Calculating Story Points

While story points are a subjective measure and can vary between teams, the following steps outline a common approach to calculating story points:

1. Define a Baseline Story: Start by identifying a user story or task that serves as a baseline reference for estimating story points. This baseline story should be of medium complexity and effort, serving as a benchmark for comparison.

2. Use a Relative Scale: Adopt a relative scale for story points, such as the Fibonacci sequence (1, 2, 3, 5, 8, 13, etc.) or a modified T-shirt sizing scale (XS, S, M, L, XL). Each point on the scale represents a relative level of effort and complexity.

3. Comparative Estimation: With the baseline story established, compare other user stories or tasks to the baseline story and assign story points based on their relative complexity and effort. Consider factors such as technical challenges, dependencies, and unknowns when making comparisons.

4. Group Consensus: Story point estimation is a collaborative effort involving the entire team. Conduct estimation sessions where team members discuss and debate the complexity of each user story, reaching a consensus on the appropriate story points.

5. Iterative Refinement: Story point estimation is an iterative process that improves over time. As teams gain more experience and data from past sprints, they can refine their estimation process and calibrate their understanding of story points.

Impact of Factors on Estimate

Amount of Work

Consider the example of developing web pages. A page with 100 fields may not necessarily be 100 times more effort than one with just one field due to economies of scale.

Risk and Uncertainty

Unclear requirements or dealing with risky technical challenges should be reflected in the estimate.

Complexity

A web page with interactive fields, validations, and complex logic is more challenging and time-consuming to implement compared to a simple page with the same number of fields.

Conclusion

While understanding story points in Agile development can be challenging, grasping how they represent effort impacted by the amount of work, complexity, and any risk or uncertainty involved is crucial. By considering these factors, teams can provide more accurate estimates and better manage their development processes.