I have been asked many times why not to use linear sequence. The reason not to use linear numbers I that linear scales do not capture the complexity and uncertainty involved in developing user stories. The complexity is captured by using a Fibonacci sequence such as: 1, 2, 3, 5, 8, 13, 21, 34, 55, 89.

It is hard to perceive a difference between stories with consecutive scores like 5 and 6 or 7 and 8. The human mind perceives a difference between 5 and 8 story points or 13 and 21 story points. The fact that Fibonacci values are further apart implies that we are forced to make a choice between the amount of significant effort a task will take to complete.

Moreover, it is difficult to establish a ratio between a 5 and 6 than 5 and 8 or 8 and 13. The fact that the intervals between values is increasing forces the mind to perceive a visible difference in magnitude as well.

While estimating work using story points, a point value is assigned to each item. The values of story point are insignificant; the most significant part of story points is the relative ratio of values. A story with 2 story points should require twice as the work effort as a story with one story point. A story with 2 story points should also require two-thirds the work effort as compared to a story with 3 story points. The calculation of effort of work involved in completing an item from product backlog is nonlinear.

To find a valid sequence to use for Story Points, the characteristics a sequence need to have includes base values, consistent ratios, and the sequence needs to be nonlinear.

The use of Fibonacci number in assigning story point is preferred because Fibonacci numbers are nonlinear and provides a sequence based on base values.

The Fibonacci sequence includes

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144

The sequence F[n] of Fibonacci numbers is defined by the recurrence relation:

F[n]=F[n-1]+F[n-2]

with seed values F[1] = 1 and F[2] = 1

By definition, the first two numbers in the Fibonacci sequence are either 1 and 1, or 0 and 1, depending on the chosen starting point of the sequence, and each subsequent number is the sum of the previous two.

If a User story is broken into parts to assign story points based on Research Regarding the Story, Amount of Effort, Complexity of Work, and Risks and Uncertainty. Each part can be assign values from the Fibonacci scale and the resulting value will be the combined effort required to complete the task.

Fibonacci sequence serves as the most adaptable scale to use for Story Points.

Author

Jagmeet Singh writes about Technology and Business on W3Courses.com. Jagmeet is the owner of Parallel Exchange and developed Phonora Photo Galley software product. In his spare time he enjoys photography and loves to travel.

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Agile, Scrum, Story Points

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