Schedule Buffers
To inject a buffer into the project schedule, the level of uncertainty needs to be identified. We should not randomly apply padding into the schedule, rather we should establish a valid range. To be more accurate with our uncertainty calculation, we need to start with two distinct numbers for estimation purposes.
- Our best uncertainty estimate is the 50%, which mean that there is a 50% chance that the project is finished on time and a 50% change that it won’t be.
- The worst uncertainty estimate is the 90%, which represents a 90% certainty regarding the time needed to complete a task. The additional time in-between the estimates are referred to as a local safety value.
If we add up all local safety values and use them as buffers, it will be inaccurate because it’s not probable that things will go incorrectly to this extent. Using two estimates is a better approach because it represents the uncertainty in the estimate and this allows us to come up with the risk linked to each user story. When we buffer our project to our 90% certainty estimate, we need a buffer that has two standard deviations. This means that we calculate the following:
- Determine the local safety value for each feature
- Square each local safety value
- Total all squared local safety estimates
- Calculate the square root of the total
- The residual number is the buffer estimate and is added to the initial estimate to calculate a range.
Recommended Further Reading
The following materials may assist you in order to get the most out of this course: