Why is the Fibonacci series used in flexible scheduled poker?

Question

When evaluating the relative size of user stories in agile software development, team members should evaluate the size of user stories as 1, 2, 3, 5, 8, 13, .... Thus, the estimated values ​​should resemble Fibonacci series. But I wonder why?

The Wikipedia description of http://en.wikipedia.org/wiki/Planning_poker contains a cryptic sentence:

The reason for using the Fibonacci sequence is to reflect the inherent uncertainty in evaluating larger items.

But why should uncertainty arise in larger objects? Is uncertainty not higher if we take fewer measurements, that is, if fewer people value the same story? And even if the uncertainty is higher in larger stories, why does this imply the use of a Fibonacci sequence? Is there a mathematical or statistical reason? Otherwise, the use of the Fibonacci series for evaluation seems to me the science of CargoCult.

Answer 1

The Fibonacci series is just one example of an exponential rating scale. The reason for using the exponential scale comes from information theory.

The information that we get from the assessment grows much slower than the accuracy of the assessment. In fact, it grows as a logarithmic function. This is the reason for the higher uncertainty for larger elements.

Determining the optimal base of an exponential scale (normalization) is difficult in practice. A base corresponding to the Fibonacci scale may or may not be optimal.

Here is a more detailed explanation of the mathematical rationale: http://www.yakyma.com/2012/05/why-progressive-estimation-scale-is-so.html

Answer 2

Of the first six numbers of the Fibonacci sequence, four are the first. This limits the ability to split the task equally into smaller tasks so that several people work on it in parallel. This can lead to a misconception that the speed of a task can scale in proportion to the number of people working on it. The 2 ^ n series is most vulnerable to such a problem. In fact, the Fibonacci sequence makes you reevaluate smaller tasks.

Answer 3

According to this flexible blog

"because they are growing at about the same speed as we humans can perceive significant changes in magnitude.

Yes, right. I think this is because they add an atmosphere of legitimacy (Fibonacci! Math!) To what is essentially a very high-level randomized (non-indicative) exercise (which matters).

But you can get the same results using the size of the t-shirt ...

Answer 4

You definitely want something exponential so that you can express any amount of time with a constant relative error. The accuracy of your assessment will also likely be proportional to your assessment.

So you want something: a) with integers b) exponential c) easy

Now why Fibonacci instead, 1 2 4 8? I guess this is because fibonacci is growing slower. It is in gold, and gold = 1.61 ...

Answer 5

The Fibonacci sequence is just one of several that are used in poker project planning.

It’s hard to accurately estimate large units of work, and it’s easy to get bogged down in hours against discussing days if your numbers are too “realistic”.

I like the explanation http://www.agilelearninglabs.com/2009/06/story-sizing-a-better-start-than-planning-poker/ , namely the Fibonacci series is a set of numbers that we can intuitively distinguish between them as different quantities

Answer 6

I use Fibonacci for several reasons:

• As the task grows, the details become harder to understand.
• Assessment of a task is the number of hours for everyone in a team to complete a task.
• Not everyone on the team will have the same amount of experience for a particular task, which also adds uncertainty.
• A person gets tired from a larger and potentially more complex task. While the task, which is doubly complex, is solved twice for the computer, it can take a little more for the developer.

As we add up all the uncertainties, we are less sure about what the clock should be. It becomes easier if we can simply measure if this task is bigger / smaller than the other, where we have already evaluated. As we increase the size / complexity of the task, the effect of uncertainty also increases. I would love to rate 13 hours for a task that seems twice as large as the one I already rated at 5 hours.