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Responsibility Chart (see Figure 4-3). 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
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
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This document was uploaded on 09/27/2013.
- Fall '13