After the project team has created the WBS, each activity is reviewed and evaluated to determine the duration (how long it will take to accomplish from beginning to end) and what resources (time, materials, facilities, and equipment) are needed. An estimate is an educated guess based on knowledge, experience, and inference—the process of deriving conclusions based on assumptions. The accuracy of the estimate is related to the quality of the knowledge and how that knowledge is applied. The person with the most knowledge may not be the most objective person to provide duration estimates. The person responsible for the work may also want to build in extra time. Multiple inputs into the duration estimate and a more detailed WBS help reduce bias—the making of decisions based on a prejudged perspective.
The unit of time used to develop the activity duration is a function of the level of detail needed by the user of the schedule. The larger and more complex the project, the greater the need for detail, which usually translates into shorter durations for activities.
Duration Estimate for Training
On a new plant start-up, the plant manager may need to know when the new employees will start training, when they will be fully trained, and when they can begin working in the plant. The plant human resources manager may need to know what skills workers need and how much time each training class will take. The schedule detail the HR manager needs will include activities to locate facilities, schedule training, write contracts for trainers, and manage the initiation of training classes. The trainer will need an even greater level of detail, which could be measured in days or even hours.
On our John’s move example, the project schedule may have been just as effective without detailing the packing of the individual rooms in the old apartment. If we deleted these items, would John know when he needed to pack each one of these rooms? If the answer is yes, then we may not need that level of detail.
The activity duration is the length of time the activity should take to complete from beginning to end. The unit of duration is typically working days but could include other units of time such as hours, weeks, or months. The unit chosen should be used consistently throughout the schedule.
An important event, such as a ground-breaking ceremony or receipt of occupancy from the building inspector, is called a milestone. A milestone has no duration or resources. It is simply an indicator of an important point in the project.
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