Project Management. Dr Jae K. Shim

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       Estimating Time, Costs, and Resources

      Once the work is broken down, you can estimate how long it will take. But how? Suppose you ask how long it will take to sort a thoroughly shuffled standard deck of playing cards 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 felling 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 an answer. People generally give answers ranging from two minutes to ten minutes. Tests indicate that about three minutes is average for most adults.

      Suppose, however, the same task was given 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 be that comfortable with counting. This leads to a very important conclusion: you cannot do a time or cost estimate without considering who will actually perform the task. Also, you must base the estimate on historical data or a mental model. Historical data are best.

      Generally average times are used to plan projects. That is, if it takes three minutes on average for an adult to sort a deck of cards, three minutes would be a good estimate to use of how long it will take during execution of my project. Naturally, when using averages, some tasks will take longer than the time allowed and some will take less. Ultimately, however, they should all 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.