Estimating Time Costs And Resources

Once the work is broken down, you can estimate how long it will take. But how do you do this? Suppose I ask you how long it will take to sort a well-shuffled deck of playing cards into numerical order by suit. How would you answer that question?

The most obvious way is to actually sort the deck several times and get a feeling for how long it takes. If you don't have a deck of cards handy, you might think about it, imagine how long it would take, and give me an answer. People generally suggest anywhere from two to ten minutes. My tests indicate that about three minutes is the average for most adults.

Figure 4-3 A project responsibility chart.

Suppose, however, that we were to give the cards to a child about four or five years old. It might take a lot longer, as the child is not that familiar with the sequence in which cards are ordered and perhaps is not even that comfortable with counting yet. We therefore reach a very important conclusion: you cannot do an estimate without considering who will actually perform the task. Second, you must base the estimate on historical data or on a mental model. Historical data are best.

Parkinson's Law: Work expands to take the time allowed.

We usually 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 would take during execution of my project. Naturally, some tasks will take longer than the time allowed and some will probably take less. Overall, they should average out.

We must be careful not to penalize workers who perform better than expected by loading them down with excessive work.

That is the idea, anyway. Parkinson's Law discredits this notion, however. Parkinson said that work always expands to take the time allowed. That means that tasks may take longer than the estimated time, but they almost never take less. One reason for this phenomenon is that when people find themselves with some time left, they tend to refine what they have done. Another is that if they turn work in early, they may be expected to do the same work faster the next time, or they may be given additional work to do. This possibility discourages people from handing work in ahead of time; if they are penalized for performing better than the target, they will quit doing so.

We also have to take into account variation. If the same person sorts a deck of cards over and over, we know the sort times will vary. Sometimes the sorting will take two minutes; other times it will take four. The average may be three, but we 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 reason? 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.


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