Work and Duration Estimation

Micro Learning Unit

Estimation of the work volume and time for each task can be done in a variety of ways: according to work or time—depending on the type of task.

Variable Duration Tasks are tasks for which the duration depends on the number and type of resources allocated for their completion. Estimating this type of task should be done based on the amount of work required. Once resources are assigned to the task, its duration can be derived using the following formula:

Work / Units (number of resources) = Duration

For example: Painting an apartment requires forty hours of work by an experienced painter. The duration of the task depends on the number of painters assigned to it. One experienced painter can paint the apartment in five working days. Two experienced painters can paint the apartment in two and a half days. An experienced painter working part-time or an inexperienced painter can paint the apartment in ten working days.

Fixed Duration Tasks are tasks for which duration does not depend on the number or type of resources assigned for their completion, however, the cost of the task does. Estimating this type of task would be done based on projected task duration. Once resources are assigned to the task, its total cost can be calculated using the following formula:

Duration x Units (number of resources) = Work

For example: It takes a fixed amount of time to wash a car in an automatic car wash. However, cleaning the car’s interior and drying the car are tasks that can be done by one or more workers. In this case, the sum total of the work and the cost of the task will change depending on how many workers are assigned to it.

Remember that the estimated task duration is a net time estimate and not its actual duration. To calculate its actual duration, the work plan must also take into consideration weekends, holidays, vacations, and any other days during which no work will be performed. It is also important to take into account the fact that most human resources will not dedicate 100% of their time to a single task. There will always be distractions in the background—meetings, support activities for previous tasks, and so on. Therefore, it is recommended that human resources not be assigned based on maximum possible efficiency for each task. Rather, time must also be allocated to support activities that do not appear in the project’s work plan.

Common ways for estimating task work or duration:

Estimates based on prior experience
A professional with relevant prior experience estimates the work or duration based on his experience with similar tasks. As part of this process, each task will be broken down into smaller parts, then the effort required to complete each part of the task will be estimated. Ideally, the estimator will also be the one executing the task, so that the estimate will form the basis of a strengthened commitment towards the work. It is considered best practice to run the estimates by at least one other person in order to validate them. If the organization has documentation of similar relevant work previously undertaken for other projects, this data should be utilized to arrive at estimates that are more accurate, based on practical experience.
Team estimates
A special team meeting should be convened specifically to generate work estimates. The project manager presents each task, each team member writes down his estimate of the work, and then all the estimates are read aloud and discussed. The team decides together on the most appropriate estimate for each task. Many misunderstandings regarding the tasks and their scope are discovered during such meetings. A discussion at this stage ensures that everyone is on the same page concerning the content and meaning of each task. This process is far from quick but it is very efficient and enables a deeper understanding and thorough agreement regarding the project’s content.
Parametric estimates
This method is particularly suitable for tasks that can be (or must be) quantified parametrically such as area, height, number of components, complexity, etc. In such cases, it is possible to provide much more accurate estimates. However, the estimation process might be longer and more complex than expected.
3 points estimation
This method is based on a weighted calculation of three estimates: an optimistic estimate, a pessimistic estimate and the most likely estimate available. For this method, too, input should be obtained from experienced professionals. Once the estimates are generated, they are weighted as follows: (1 x pessimistic estimate) + (4 x most likely estimate) + (1 x optimistic estimate)/6. In this method, the estimator is asked for a pessimistic estimate—one that takes into account unforeseen events that might increase the duration needed to complete the project—alongside an optimistic estimate—one that assumes that everything goes as planned, and perhaps even better than planned. Finally, the estimator is asked for his most reasonable estimate. This estimate is assigned the highest weight in the calculation above.
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