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Why Do Agile Teams Use the Fibonacci Scale for Estimation?

Why Do Agile Teams Use the Fibonacci Scale for Estimation? 

Project estimation, while fundamental to the success of any venture, has often been likened to gazing into a crystal ball. You never truly know how accurate your predictions are until you're well into the project. The estimation accuracy at Microsoft is improved using relative points instead of hours. The tech giant approaches project estimation, especially in iterative development scenarios, by comparing past work items to future ones. This approach has proven more accurate and less time-consuming than the alternative. So, while uncertainties are part of project estimations, the right strategies and tools can significantly narrow down the margin of error.  


In the world of Agile, accurate estimation is essential for managing work, setting client expectations, and delivering value in an iterative manner. If you're familiar with Agile methodologies, you've likely come across the Fibonacci sequence when estimating tasks. But why Fibonacci? Let's dive into the rationale behind it. 

1. Human Limitation in Perceiving Differences: 

Humans are generally good at distinguishing between small numbers. For example, we can easily tell the difference between tasks that take 2 hours and those that take 3 hours. But when it comes to larger numbers, our perception starts to get fuzzy. Can we really differentiate between tasks that take 13 hours versus 14 hours? The Fibonacci sequence captures this human limitation, emphasizing clear distinctions at the lower end and blending distinctions as numbers grow larger. 

2. Uncertainty Grows with Size: 

Larger tasks tend to carry more unknowns and risks. The jumps between numbers in the Fibonacci sequence inherently reflect this growing uncertainty. When a task is estimated to be an 8 instead of a 5, it’s not just 3 units more in work, but also an acknowledgment of increased complexity and unpredictability. 

3. Discourages False Precision: 

Using the Fibonacci sequence prevents teams from falling into the trap of false precision. When estimates get too granular, they give an illusion of accuracy and certainty which doesn't really exist in complex projects. By using Fibonacci numbers, Agile teams acknowledge that they can't predict work down to the minutest detail. 

4. Simplifies Decision Making: 

When faced with estimating tasks, having a fixed set of numbers to choose from (like the Fibonacci sequence) streamlines decision-making. This reduces analysis paralysis and encourages team members to converge on a common estimate more quickly during planning poker or estimation sessions. 

5. Encourages Decomposition of Larger Tasks: 

In Agile, breaking tasks down into smaller, more manageable chunks is encouraged. If a task is estimated to be at the higher end of the Fibonacci scale, it's a cue for the team to consider if the task can be broken down further. This promotes better understanding, clearer scope, and more accurate estimates. 

6. It's Proven and Popular: 

Simply put, many Agile teams have found success with the Fibonacci sequence. Its adoption has made it a familiar tool, leading to smoother estimation sessions and more consistent results across the industry. 

7. A Balance Between Linear and Logarithmic Scales: 

While the Fibonacci sequence grows in a manner that might seem exponential, it actually offers a balance that is somewhere between a strict linear and a logarithmic scale. This balance captures the essence of both small tasks (where linear differences matter) and large tasks (where proportional differences matter more). 

In Conclusion: 

The Fibonacci sequence, in its unique way, mirrors the intricacies of software development and project work. By resonating with human psychology, emphasizing relativity, and acknowledging the inherent uncertainties in complex projects, the Fibonacci scale has become a powerful tool for Agile teams around the world. So, the next time you're estimating, consider embracing the Fibonacci sequence and harnessing its many advantages. 

1 Comment

Jan 27

Also - Fibonacci is copyright free. Many of the popular planning deck sequences are actually have copyrights filed.


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