Dynamic range, abbreviated DR or DNR, is the ratio between the largest and smallest possible values of a changeable quantity.
DRE is an agile estimation technique intended for use in the estimation of size and risk associated with IT requirements implementation. The dynamic range estimation (DRE) method provides a simple yet powerful visualisation tool for assessing requirements’ size and complexity and allows for visual comparison and trade-off between solution alternatives.
DRE differs from other estimation techniques in that it also provides the means to communicate the potential for those estimates to change over time.
A quick example…
Let’s assume you are estimating the scope of a potential user requirement. This may be expressed in the style of a ‘user story’:
“As an online shopper I want to be able to add items to my basket so that I can purchase those items together.”
We might estimate the effort to implement this to be ten days. We may go further and describe whether we mean elapsed days or ideal days. We may also have arrived at this time estimate by estimating the complexity of the requirement and deriving the duration it would take to implement it. Regardless of the unit of measure we use to provide the estimation, we arrive at the estimate:
“Add Item to Basket” = 10 Days Effort for 1 Team
This information has significance to our customer or project leader, and this information creates a level of expectation. Such estimates are used to coordinate activities such as release schedules and training. DRE adopts the perspective that there is a vital piece of information missing from this estimate, and so explicitly asks the question:
“What level of confidence should I place in this estimate?”
Importantly, with DRE we ask this question of the people most likely to provide us with the highest quality information, i.e. the team that provided the original estimate.
Estimation is an important tool for self-organising teams. Estimation also provides essential information for people who rely on the output from those teams. Regardless of the audience or purpose, when presented with an estimate we should always ask this question because an estimate does not represent a commitment. It is an inherent quality of any estimate that it includes a degree of uncertainty; with DRE we express this openly and explicitly:
“Add Item to Basket” = 10 Days Effort for 1 Team (+50% / -25%)
This offers far more insight into how the team tasked with implementation view the problem than a single time or complexity-based estimate. This tells us two things:
1) Based upon current understanding, what the team believe the effort for implementation will be.
2) The potential for change of this estimate with greater understanding of the problem.
We can then employ some simple communication tools and templates to express this visually. We can also use our template to derive the ratio between our maximum and minimum estimate, in this case, 2 to 1.
One interesting point to note regarding this visualisation is the maximum scale of twenty-five days. We can use this scale to set a limit on the maximum size work item we can responsibly deliver against as a team. To relate this principle to a time-boxed iteration of two weeks, the maximum scale would be ten, representing ten working days. DRE does not specify what the maximum size should be but it does specify that one should exist and, the smaller this number, the more consistent your estimation will be.
By employing the maximum size rule, we can visually compare the estimated size of our requirement against that maximum scale, and also the potential this requirement has to extend beyond it. By placing multiple requirement estimates next to each other, we can also compare the relative size and uncertainty between multiple requirement estimates. When reviewing our estimates it is important to keep in mind: the more regular the shape of the triangle, the greater our confidence in the estimate; the more irregular the shape of the triangle, the greater the uncertainty in our estimate.
This has been a quick introduction into DRE. For a more in-depth view, take a look at the ‘Getting Started with Dynamic Range’ section of this site. DRE is easy to understand and to communicate to others. All you need to get started with DRE is a pen and paper or a whiteboard. We’ve also included some estimation templates that were used in putting together the examples on this site.