I have a long vendor task in my project that has padding built into it, yet they are unlikely to deliver early. In other words, their 50/50 duration is pretty close to their low-risk or worst-case duration. How do I get ProChain to take this into account so that it doesn’t create a huge buffer to protect it?
ProChain sizes the buffer based on the amount of variability in the tasks it is protecting against—it’s a function of the variability in the tasks, not the duration of the tasks. For example, if the tasks are guaranteed to be delivered on schedule, no buffering would be needed. ProChain calculates the variability of a task as the difference between the low-risk duration (the Duration1 field is the default) and the Focus duration (the Duration field). If you do not enter a low-risk duration (or you enter an invalid one) then ProChain will assume that the low-risk duration is twice the focus duration.
Let’s look at an example. If you have a 10w duration task and you leave the low-risk duration at 0, then ProChain will use 20w as the low-risk duration. The variability will be 20w – 10w or 10w. 50% buffers (using the percentage sizing method) will result in 5w of buffering associated with this task. If you are pretty sure that the vendor won’t slip by more than 2w, you would set the Duration1 field to 12w. The variability is 2w and the result will be 1w of buffering—a reduction of 4w compared to not entering a low-risk duration.
- On July 20, 2017