Carl Bruiners Agile / IT Development Consultant

Cone of uncertainty

Cone Of Uncertainty

Above is a cone of uncertainty, this image demonstrates how larger stories come with greater risk when not broken down further.

Small stories between 1-3 pt’s shouldn’t have a grey area because for the team to know that a story is so small they should have a good grasp on what is required to deliver that story. I have placed the 5pt story on the line border of having grey matter, as though 5pt stories are of a size where the team should know whats required to complete the story, I have found in practice that this is not always the case and often 5pt stories end up being more like a 6pt’ish story .

As the story sizes increase, so does the grey area, and the grey area is not directly relational to the ideal inner cone. Get your scrum master to keep track of estimations, the actual time taken to deliver and from this you will be able to calculate your teams multiplier for the ‘grey area’. You can then use this in your sprint planning sessions as a safety buffer.

How do you minimise the ‘grey area’? Due to the nature of large stories it is not possible to remove the grey area completely, but you can utilise methods to reduce the ‘grey’. Having well defined stories and story acceptance criteria all help reduce uncertainty around a story. Though I’d rather spend time out of a meeting, if you have a 10 pt story and your grey area multiplier suggests a 3pt buffer, but a meeting would only take 30 minutes to help add clarity to your story, do the meeting as this may reduce the 3pt buffer. Do all that you can to reduce the grey area, but accept that you will never be in a position to completely remove this grey matter.