Estimating Time, Costs, and Resources
Once the work is broken down, you can estimate how long it will take. But how? Suppose I ask you how long it will take to sort a standard deck of playing cards that has been thoroughly shuffled into numerical order by suit. How would you answer that question?
The most obvious way would be to try the task several times and get a feeling for it. But if you didn’t have a deck of cards handy, you would probably think about it, imagine how long it would take, and give me an answer. People generally give me answers ranging from two minutes to ten minutes. My tests indicate that about three minutes is average for most adults.
An estimate can be made only by starting with the assumption that a certain resource will be assigned.
Suppose, however, we gave the cards to a child about four or five years old. It might take a lot longer, since the child would not be that familiar with the sequence in which cards are ordered, and perhaps not yet even that comfortable with counting. So we must reach a very important conclusion: You cannot do a time or cost estimate without considering who will actually perform the task. Second, you must base the estimate on historical data or a mental model. Historical data are best.
Parkinson’s Law: Work expands to fill the time allowed.
Generally we use average times to plan projects. That is, if it takes three minutes on average for adults to sort a deck of cards, I would use three minutes as my estimate of how long it will take during execution of my project. Naturally, when I use averages, in reality some tasks will take longer than the time allowed and some should take less. Overall, however, they should average out.
That is the idea, anyway. Parkinson’s Law discredits this notion, however. Parkinson said that work always expands to fill the time allowed. That means that tasks may take longer than the estimated time, but they almost never take less. One reason is that when people find themselves with some time left, they tend to refine what they have done. Another is that people fear that if they turn work in early, they may be expected to do the task faster the next time or that they may be given more work to do.
We must be careful not to penalize workers who perform better than expected by loading them down with excessive work.
This is a very important point: if people are penalized for performing better than the target, they will quit doing so. We also have to understand variation. If the same person sorts a deck of cards over and over, we know the sort times will vary. Sometimes it will take two minutes, while other times it will take four. The average may be three, but we may expect that half the time it will take three minutes or less and half the time it will take three minutes or more. Very seldom will it take exactly three minutes.
An exact estimate is an oxymoron!
The same is true for all project tasks. The time it takes to perform them will vary, because of forces outside the person’s control. The cards are shuffled differently every time. The person’s attention is diverted by a loud noise outside. He drops a card while sorting. He gets tired. And so on.
Can you get rid of the variation? No way.
Can you reduce it? Yes—through practice, by changing the process by which the work is done, and so on. But it is important to note that the variation will always be there, and we must recognize and accept it.
The Hazards of Estimating
Consider the case of Karen. One day her boss stopped by her desk at about one o’clock. “Need for you to do an estimate for me,” he told her. “Promised the Big Guy I’d have it for him by four o’clock. You with me?”
Karen nodded and gave him a thin smile. The boss described the job for her. “Just need a ballpark number,” he assured her and drifted off.
Given so little time, Karen could compare the project her boss described only to one she had done about a year before. She added a little for this and took a little off for that, put in some contingency to cover her lack of information, and gave the estimate to the boss. After that, she forgot all about the job.
Two months passed. Then the bomb was dropped. Her boss appeared, all smiles. “Remember that estimate you did for me on the xyz job?”
She had to think hard to remember, but, as her boss droned on, it came back to her. He piled a big stack of specifications on her desk. “It’s your job now,” he told her and drifted off again into manager dreamland.
As she studied the pile of paper, Karen felt herself growing more concerned. There were significant differences between this set of specs and what her boss had told her when she did the estimate. “Oh well, I’m sure he knows that,” she told herself.
Finally she managed to work up a new estimate for the job on the basis of the real specs. It was almost 50 percent higher than the ballpark figure. She checked her figures carefully, assured herself that they were correct, and went to see her boss.
He took one look at the numbers and went ballistic. “What are you trying to do to me?” he yelled. “I already told the old man we would do it for the original figure. I can’t tell him it’s this much more. He’ll kill me.”
“But you told me it was just a ballpark number you needed,” Karen argued. “That’s what I gave you. But this is nothing like the job I quoted. It’s a lot bigger.”
One of the primary causes of project failures is that ballpark estimates become targets.
“I can’t help that,” her boss argued. “I already gave him the figures. You’ll have to find a way to do it for the original bid.”
Naturally, you know the rest of the story. The job cost even more than Karen’s new estimate. There was a lot of moaning and groaning, but, in the end, Karen survived. Oh, they did send her off to a course on project management—hoping, no doubt, that she would learn how to estimate better in the future.
Guidelines for documenting estimates:
- Show the percent tolerance that is likely to apply.
- Tell how the estimate was made and what assumptions were used.
- Specify any factors that might affect the validity of the estimate (such as time—will the estimate still be valid in six months?).
Could you fault Karen for anything? Well, perhaps. If she failed to tell the boss that a ballpark estimate may have a tolerance of perhaps ±25 percent but that the margin of error can range from –10 percent to +100 percent, then she allowed him to think that the estimate was better than it was. Also, she should have documented all working assumptions, explaining how she did the estimate, what project she had used for comparison, and so on. Then, if management still pulled a whammy on her, at least she would have had some protection. In fact, it is impossible to make sense of any estimate unless these steps are taken, so they should be standard practice.
Consensual Estimating
In recent years, a new method of estimating knowledge work has been developed that seems to work better than older techniques. Rather than have individuals estimate task durations, the new method asks at least three people to estimate each activity in the project that they know something about. They do this without discussing their ideas with one another. They then meet to find out what they have put on paper. In a typical situation, there may be a range of times, such as, for example, ten days, twelve days, and thirty days, in which two of the estimates are close together, but one is very different. How do you handle the discrepancy?
The best approach is to discuss what each person was considering when he or she made the estimate. It may be that the person who put down thirty days was thinking about something that the other two had overlooked. Or, conversely, they may convince the thirty-day person that his number is way too high and get him to come down to a figure nearer their estimates. In any case, they try to arrive at a number that they all can support. This is called consensus.
There are three advantages to this approach. First, no one person is on the hook for the final number. Second, inexperienced people learn to estimate from those more experienced. Third, they are likely to collectively consider more issues than any one person would do working alone. For that reason, you are more likely to get an accurate estimate, although it is important to remember that it is still not exact!
Improving Estimating Ability
People cannot learn unless they receive feedback on their performance. If you went out every day and ran 100 yards, trying to improve your speed, but you never timed yourself, you would have no idea whether you were getting better or worse. You could be doing something that slowed you down, but you wouldn’t know it. In the same way, if you estimate task durations but never record the actual time it takes to do the task, you are never going to get better at estimating. Furthermore, you have to track progress by recording times daily. If you record times once a week, I can promise you that you will be just guessing, and that won’t be helpful.
Key Points to Remember
|