Bottom-Up Estimating
Bottom-up estimates are the cost and duration of individual work items in hours, which is summarized or combined, resulting in a project total. The cost and accuracy are driven by the size of the individual work items. Smaller work items increase both cost and accuracy to the project estimate.
Bottom-up estimates are considered to be the most accurate and allow for the integration of activities that occur within an organization. A good bottom-up estimate demonstrates a detailed understanding of the work to be done on a project.
A key challenge of these estimates is that people providing the estimates might add reserve to individual activities. That is why a project manager must explain to the team that the LOE, availability, and productivity have been included in the estimate for individual tasks. The bottom-up approach is the financial equivalent of the scientific method of discovery. Where the scientific method takes the whole and decomposes it to its smallest parts, the bottom-up method assigns estimates to the smallest parts and then composes them back to the whole.
Estimation Methods
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