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The most commonly used techniques for creating project estimates are analogous estimates, bottom up estimates, three point estimates, and using a parametric model.
The most commonly used techniques for creating project estimates are analogous estimates, bottom up estimates, and using a parametric model. All of these techniques rely on some level of expert judgement and at least a tentative plan for how the work will be done.
When to use
Estimates are used to when planning a project or when replanning a project due to a change. This will occur at the beginning of a project or project phase.
There are many techniques that can be used. Listed below are the most common:
This technique bases the estimate on the experience of a similar project. It relies on someone having done this type of work before. This is a very quick technique, but the estimate is very dependent upon who is doing the estimating and their experiences.
Bottom up estimate
This estimate requires that the activities of the project be decomposed into very small “micro-tasks.” Smaller tasks are usually easier to estimate accurately because all of the work is understood and you can normally find someone who has done a similar “micro-task” and can provide you with an analogous estimate. An entire project estimated in this manner will have an accurate estimate, but it can take a long time – sometimes months – to decompose all the tasks into “micro-tasks”.
In this case the experience of many projects has been codified into a formula. The formula uses one or two parameters that are easily determined during project planning. By entering these parameters into the formula, a cost estimate or time estimate is derived. For instance, the time estimate on a shipping task may use a distance parameter in the formula.
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