The Fibonacci Sequence is a mathematical sequence where each number is the sum of the two preceding ones, typically starting with 0 and 1. The sequence looks like this:
0, 1, 2, 3, 5, 8, 13, 21, 34, and so on.
In the context of Agile development, the Fibonacci sequence is often used as a tool for estimating the effort or complexity of user stories or tasks during sprint planning. The use of Fibonacci numbers in Agile methodologies, particularly Scrum, helps teams to better assess and compare the relative size of different work items and make more informed decisions about how to allocate time and resources.
Why Use Fibonacci in Agile?
Relative Estimation: The Fibonacci sequence is a helpful way to make relative estimates about the complexity of user stories. Instead of assigning arbitrary numbers, teams can assign Fibonacci values to indicate how much effort or time a task will likely take compared to others.
Non-linear Progression: As the numbers increase, the difference between them grows. This mirrors real-world complexity—tasks that are larger in scope tend to have exponentially increasing uncertainty, so estimating them requires more effort. For example, a task that is rated as 3 is clearly smaller in complexity than one rated as 8, and the difference between 8 and 21 is even larger.
Simplicity in Decision Making: The Fibonacci scale simplifies decision-making for teams. It encourages them to focus on making rough, high-level estimations rather than overthinking or getting bogged down in exactness, which can be counterproductive when trying to estimate work.
Avoiding Precision Traps: Traditional estimating methods may lead to over-precision in estimates. By using a sequence like Fibonacci, it becomes easier to categorize tasks in broader ranges and avoid debates over small differences that aren’t meaningful in the context of development.
How Fibonacci is Used in Agile
In Agile, particularly in Scrum, Fibonacci numbers are used during story pointing to estimate the effort, time, or complexity of tasks or user stories. Here’s how it typically works:
1. Story Points:
Teams use story points as a measure of effort or complexity, with each number in the Fibonacci sequence (1, 2, 3, 5, 8, 13, etc.) representing a different level of complexity. The numbers are usually assigned in relation to the smallest task or user story, and each successive number represents a progressively larger effort or complexity.
For example:
- 1 point: A simple task that can be completed easily (e.g., updating a line of text).
- 3 points: A task that requires moderate effort or minor complexity (e.g., adding a new button with limited functionality).
- 5 points: A task of average complexity (e.g., adding a form with validation).
- 8 points: A more complex task (e.g., implementing a new feature with multiple dependencies).
- 13 points: A highly complex or large task that requires substantial effort (e.g., building a complex report generator).
2. Planning Poker:
One of the most common methods of applying the Fibonacci sequence in Agile is through a technique called Planning Poker. In Planning Poker, each team member is given a set of cards with Fibonacci numbers (or a modified Fibonacci sequence like 1, 2, 3, 5, 8, 13, 20). The process works as follows:
- The Product Owner presents a user story to the team.
- Team members discuss the user story to gain a shared understanding.
- Each team member selects a card that represents their estimate of the story’s complexity or effort.
- Once everyone has chosen a card, the estimates are revealed at the same time.
- If there’s a wide variance in estimates, the team discusses their reasoning, and the process is repeated until consensus is reached.
3. Velocity:
Teams also use velocity to track the number of story points they complete in each sprint. Velocity helps teams to forecast how much work they can handle in future sprints, based on historical data. By using Fibonacci numbers, it becomes easier to assess how much effort the team can reasonably complete in a sprint.
Advantages of Using Fibonacci for Estimation
Encourages Team Consensus: Because the Fibonacci scale is non-linear, it forces the team to discuss the differences between task estimates and helps arrive at a consensus through collaboration.
Simplifies Estimations: The use of a small set of discrete numbers (the Fibonacci sequence) means estimations are less detailed and more straightforward. This helps reduce confusion and makes it easier to identify how different tasks compare in terms of complexity.
Handles Uncertainty: As mentioned, Fibonacci numbers increase exponentially, which reflects the increasing uncertainty and complexity of larger tasks. This mirrors the reality of software development, where larger tasks tend to have more variables and potential challenges.
Improves Focus on Progress Over Perfection: Teams aren’t aiming for perfect, precise estimates, which is often unrealistic. The goal is to estimate “good enough” and keep moving forward, adjusting based on real feedback as the project progresses.
Example: Estimating User Stories with Fibonacci Numbers
Let’s take an example of a few user stories and how they might be estimated using the Fibonacci sequence:
User Story 1: As a user, I want to log in using my username and password.
- Estimated Points: 3 points (a basic task with moderate complexity, a common feature with clear requirements).
User Story 2: As a user, I want to view a list of all products in the store, which may be paginated or sorted.
- Estimated Points: 5 points (slightly more complex, requiring database interactions, UI elements, and testing for pagination and sorting).
User Story 3: As a user, I want to create an account, verify my email, and receive a confirmation email.
- Estimated Points: 8 points (a moderately complex task that requires email services, validation, and more testing).
User Story 4: As an admin, I want to generate a monthly sales report with detailed filters and export options.
- Estimated Points: 13 points (this is a larger task with more complexity, including data aggregation, report generation, and export functionality).
Conclusion
The Fibonacci sequence provides a useful and effective way to estimate work in Agile. By using a non-linear scale for story points, it helps teams express their relative confidence in the effort required to complete a task and facilitates discussions about the scope and complexity of user stories. While it might not be perfect, its simplicity and alignment with real-world complexity make it a valuable tool for Agile teams looking to improve their planning and forecasting processes.