Applied Software Project Management [Paperback]

Many people have referred to estimation as a “black art.”this makes some intuitive sense: at first glance,it might seem that estimation is a highly subjective process.One person might take a day to do a task that might only require a few hours of another ’s time. As a result, when several people are asked to estimate how long it might take to perform a task,they will often give widely differing answers.But when the work is actually performed,it takes a real amount of time;any estimate that did not come close to that actual time is inaccurate.

To someone who has never estimated a project in a structured way,estimation seems little more than attempting to predict the future.This view is reinforced when off-the-cuff estimates are inaccurate and projects come in late.But a good formal estimation process, one that allows the project team to reach a consensus on the estimates,can improve the accuracy of those estimates,making it much more likely that projects will come in on time.A project manager can help the team to create successful estimates for any software project by using sound techniques and understanding what makes estimates more accurate.

Elements of a Successful Estimate

A sound estimate starts with a work breakdown structure (WBS).A WBS is a list of tasks that,if completed,will produce the final product.The way the work is broken down dictates how it will be done.There are many ways to decompose a project into tasks. The project can be broken down by feature,by project phase (requirements tasks, design tasks, programming tasks,QA tasks,etc.),or by some combination of the two. Ideally,the WBS should reflect the way previous projects have been developed.

A useful rule of thumb is that any project can be broken down into between 10 and 20 tasks. For large projects (for example,a space shuttle),those tasks will be very large (“Test the guidance system ”);for small projects (like writing a simple calculator program),the tasks are small (“Build the arithmetic object that adds,multiplies,or divides two numbers ”).The team must take care in generating the WBS â€"if the tasks are incorrect,they can waste time going down a wrong path.

Once the WBS is created,the team must create an estimate of the effort required to perform each task.The most accurate estimates are those that rely on prior experience. Team members should review previous project results and find how long similar tasks in previous projects took to complete.Sources of delays in the past should be taken into account when making current estimates.Postmortem reports (see Chapter 8)are a good source of this information.

No estimate is guaranteed to be accurate.People get sick or leave the organization;teams run into unforeseen technical problems;the needs of the organization change.The unexpected will almost certainly happen.Therefore,the goal of estimation is not to predict thefuture.Instead,it is to gauge an honest,well-informed opinion of the effort required to do a task from those people in the organization who have the most applicable training and knowledge.

If two people widely disagree on how long a task will take,it ’s likely that the source of that disagreement is that each person made different assumptions about details of the work product or the strategy for producing it.In other words,any disagreement is generally about what is required to perform the task itself,not about the effort required to complete it.Forexample,given the same vision and scope document for a tool that sets the computer clock, two different developers might come up with wildly different estimates. But it might turn out that one developer assumed that the implementation would have a simple command-line interface,while the other assumed that there would be a complete user interface that had to integrate tightly with the operating system ’s control panel.By helping the programmers discuss these assumptions and come to a temporary resolution about their differences, the project manager can help them agree on a single estimate for the task.

A project manager can help the team create more accurate estimates by reducing the uncertainty about the project.The most effective way to do this is to do a thorough job creating a vision and scope document (see Chapter 2)â€"the more accurate and detailed it is,the more information the team has to work with when generating their estimate.The project manager can also ensure that the team has reached a consensus on the tasks that must be performed.Finally,the project manager can lead the team in a discussion of assumptions.

Assumptions Make Estimates More Accurate

Once the team has agreed upon a WBS,they can begin to discuss each task so they can come up with an estimate.At the outset of the project,the team members do not have all of the information they need in order to produce estimates;nevertheless,they need to come up with numbers.To deal with incomplete information,they must make assumptions aboutthe work to be done.By making assumptions,team members can leave placeholders for information that can be corrected later,in order to make the estimate more accurate.

For the estimates to be most effective,the assumptions must be written down. Important information is discovered during the discussion that the team will need to refer back to during the development process,and if that information is not written down, the teamwill have to have the discussion all over again.If an assumption turns out to be incorrect, the schedule will need to be adjusted;they will be able to point to the exact cause of the delay by showing that a documented assumption turned out to be incorrect.This will help the project manager explain any resulting schedule delay to others in the organization and avoid that source of delays in the future.The assumptions also provide a way to keep a record of team decisions,share those decisions with others,and find errors in their decisions.(The assumptions should be added to the “Assumptions ” section of the vision and scope document â€"see Chapter 2.)