Strictly speaking, the dictionary definition of estimate is correct: an estimate is a prediction of how long a project will take or how much it will cost. But estimation on software projects interplays with business targets, commitments, and control.
A target is a statement of a desirable business objective. Examples include the following:
"We need to have Version 2.1 ready to
"We need to have this release stabilized in time for the holiday sales cycle."
"These functions need to be completed by July 1 so that we'll be in compliance with government regulations."
"We must limit the cost of the
Businesses have important reasons to establish targets independent of software estimates. But the fact that a target is desirable or even mandatory does not
While a target is a description of a desirable business objective, a
is a promise to deliver defined functionality at a specific level of quality by a certain date. A commitment can be the same as the estimate, or it can be more
Distinguish between estimates, targets, and commitments.
Estimation and planning are
Estimates form the foundation for the plans, but the plans don't have to be the same as the estimates. If the estimates are dramatically different from the targets, the project plans will need to recognize that gap and account for a high level of risk. If the estimates are close to the targets, then the plans can assume less risk.
Both estimation and planning are important, but the fundamental differences between the two activities mean that combining the two tends to lead to poor estimates
poor plans. The presence of a strong planning target can lead to substitution of the target for an analytically derived estimate; project
Here are examples of planning considerations that depend in part on accurate estimates:
Creating a detailed schedule
Identifying a project's critical
Creating a complete work breakdown structure
Prioritizing functionality for delivery
Breaking a project into iterations
Accurate estimates support better work in each of these areas (and Chapter 21, "Estimating Planning Parameters," goes into more detail on these topics).
EXECUTIVE: How long do you think this project will take? We need to have this software ready in 3 months for a trade show. I can't give you any more team
members, so you'll have to do the work with your current staff. Here's a list of the features we'll need.
PROJECT LEAD: OK, let me crunch some
numbers, and get back to you.
PROJECT LEAD: We've estimated the project will take 5 months.
EXECUTIVE: Five months!? Didn't you hear me? I said we needed to have this software ready in 3 months for a trade show!
In this interaction, the project lead will probably walk away thinking that the executive is irrational, because he is asking for the team to deliver 5 months' worth of functionality in 3 months. The executive will walk away thinking that the project lead doesn't "get" the business reality, because he doesn't understand how important it is to be ready for the trade show in 3 months.
Note in this example that the executive was not really asking for an estimate; he was asking the project lead to come up with a plan to hit a target . Most executives don't have the technical background that would allow them to make fine distinctions between estimates, targets, commitments, and plans. So it becomes the technical leader's responsibility to translate the executive's request into more specific technical terms.
Here's a more productive way that the interaction could go:
EXECUTIVE: How long do you think this project will take? We need to have this software ready in 3 months for a trade show. I can't give you any more team members, so you'll have to do the work with your current staff. Here's a list of the features we'll need.
PROJECT LEAD: Let me make sure I understand what you're asking for. Is it more important for us to deliver 100% of these features, or is it more important to have something ready for the trade show?
EXECUTIVE: We have to have something ready for the trade show. We'd like to have 100% of those features if possible.
PROJECT LEAD: I want to be sure I follow through on your priorities as best I can. If it turns out that we can't deliver 100% of the features by the trade show, should we be ready to ship what we've got at trade show time, or should we plan to slip the ship date beyond the trade show?
EXECUTIVE: We have to have something for the trade show, so if push comes to shove, we have to ship something, even if it isn't 100% of what we want.
PROJECT LEAD: OK, I'll come up with a plan for delivering as many features as we can in the
When you're asked to provide an estimate, determine whether you're supposed to be estimating or figuring out how to hit a target.