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Effective Software Project Management by Robert K. Wysocki Ph.D.

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Estimating Time, Cost, and Resource Requirements

Before you can estimate duration, you need to make sure everyone is working from a common definition. The duration of a project is the elapsed time in business working days required to complete the project, activity, or task. Duration is different from effort. Effort is labor hours required to complete a project, activity, or task. Effort is always less than or equal to duration. Labor hours can be consecutive or nonconsecutive hours. It is this elapsed time that you are interested in estimating for each task. It is the true duration of the task. For costing purposes you are interested in the labor time (work) actually spent on the task.

Resource Loading versus Task Duration

The duration of a task is affected by the number of resources scheduled to work on it. I say affected by because there is not necessarily a direct linear relationship between the amount of resource assigned to a task and its duration. For example, suppose you are responsible for completing a certain programming task. You estimate that it will take 4 weeks to complete. The project manager says that it must be done in 2 weeks so she will ask another programmer to join you in the task. Will that reduce the task duration to 2 weeks? Absolutely not. There are several reasons why the relationship is not linear. Among the reasons are the need for person-to-person communications, deciding on programming conventions, deciding who will work on what, and a host of other ...

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