In the first article in this series we looked at absolute vs. relative estimation, and using an example saw how we could improve our estimation accuracy by applying relative estimation. In this article we briefly at a second reason we use a relative estimate of effort instead of time to improve our estimates.As described in Agile estimation and planning: Part 1, people are poor at absolute estimation.
Guess what. Time is an absolute value. As such, people are poor at estimating time.
Beyond the fact that people are poor at estimating in absolute values, and therefor estimating using time, there is a second problem with using time to estimate: the time required to complete a given effort varies greatly from person to person.
Again using an example, our General Manager, Kevin Sheen, is a keen runner. Each year Kevin competes in distance running activities including triathlons and marathons. If you were to ask Kevin how long it takes to run a mile I’m sure he can tell you down to the second how long it takes him to run a mile (considering, of course, the total distance to be run to establish a pace appropriate to conserve energy so that he could run the entire distance). I, on the other hand, overweight and bad knees, have no hope of running a mile. Because I don’t run frequently I also have no idea how long it would take me to go a mile. Any estimate I could provide would be both inaccurate and would clearly be much different (larger and grossly less accurate) than Kevin’s estimate.
Interestingly, however, the amount of effort (measured in calories expended) involved in transversing a mile, for both Kevin and myself, is remarkably similar. The mile is the same mile, the effort is actually the same effort; it’s just the time it takes to complete the effort varies based on our individual capabilities and characteristics.
This same principle applies equally well to systems development work as it does to running. The amount of effort required to implement a given feature is the same regardless of who performs the work (a mile is a mile), however based on the capabilities and characteristic of a given individual, the amount of time required to complete the effort can vary significantly. Since we’re often ask to estimate systems well in advance of having an identified and specific team in place to perform the work, estimating relative to individual capability is impractical and inaccurate.
Using relative effort allows us to overcome this issue.
Therefore, using an Agile estimation approach, we use a relative value of effort, not time, in developing our estimates.
