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3. The team resolves any issues or disagreements that are brought up. Since individual
estimate times are not discussed, these disagreements are usually about the tasks
themselves, and are often resolved by adding assumptions. When an issue is resolved,
team members should write clarifications and changes to the task list on their
estimation forms. This usually takes about 40 minutes for the first round, and 20
minutes for the following rounds.
4. The estimators all revise their individual estimates by filling in the next “Delta” column
on their forms. (Using a delta allows the estimators to write “+4” or “-3” to add 4 or
remove 3 from the estimate. They write the new total at the bottom of the sheet.)
This cycle repeats until either all estimators agree that the range is acceptable, the estima-
tors feel they do not need to change their estimates, or two hours have elapsed.
Each round brings the estimates closer to convergence. Figure 3-4 shows what the typical
results of an estimation session will look like. It may seem magical to the team—through a
straightforward discussion of assumptions and task definition, the team arrives at a consen-
sus that is visible on the whiteboard! This consensus is a result of clarifying these potential
ambiguities. Usually the first round brings a long discussion of missed assumptions and
changes to the task definition. In the later rounds, the moderator will play an important role
in directing the conversation toward where it will be most effective. The moderator should
look for the tasks that have the largest spread between the highest and lowest estimates. He
should lead a frank discussion of the breakdown or details of that task, as well as places
where the team might be over- or underestimating the effort for that task.
Round 40
Round 30
Round 20
Round 10
10 20 30 40 50 60 70 80
FIGURE 3-4. Converging estimate results
Disagreements often arise, but they are easier to deal with in this setting than later on,
when the project is in progress. One effective way to resolve these disagreements is to talk
about both sides of the issue, and then agree on an assumption that takes one of those
sides. It is easier to make this decision at this stage because the assumption is not perma-
nent; the team can very easily go back and change that assumption, if necessary. But writ-
ing down the assumption allows the team to show management that if this assumption
turns out to be incorrect, the estimate may no longer be accurate. This way, even though
the estimate is not perfect, the team understands why that is the case. If the team has con-
fidence that they did a complete job with the assumptions, they will have more confidence
in the value of the estimate.
After the conclusion of the estimation cycle, the moderator leads a discussion on how the
session went. The team suggests ways to improve. The moderator notes their feedback, to
include it in the final estimation report.
46 CHAPTER THREE