Estimation Techniques
Top-down vs ground up estimations
Abstract
Top-down and bottom-up are two different approaches to project estimation that are used to determine the cost, schedule, or effort required to complete a project. While top-down estimation is a high-level approach that breaks down the total project cost or effort into smaller parts, bottom-up estimation is a detailed approach that starts with the estimation of individual tasks or components and aggregates them to arrive at a total project estimate.
Top-down estimation is a quick and easy method that is based on past experience or general knowledge. It is used when there is limited information available about the project, or when the goal is to quickly arrive at a rough estimate of the project cost or effort. This method can be less accurate, as it does not consider all the specific details of the project, but it can provide a good starting point for further analysis.
Bottom-up estimation, on the other hand, is a more detailed and accurate method that is used when more information is available about the project and its components. This method requires a more in-depth knowledge of the project and its components, and can be time-consuming as it involves estimating each individual task or component. However, the benefit of this approach is that it provides a more accurate estimate of the project cost or effort, and allows for the identification of any potential risks or issues that may impact the project schedule or budget.
In practice, most organizations use a combination of top-down and bottom-up methods to arrive at a final estimate that is both accurate and efficient. Top-down estimation is used to quickly arrive at a rough estimate of the project cost or effort, while bottom-up estimation is used to refine this estimate and make it more accurate. This allows organizations to balance the need for speed and accuracy, and to arrive at a final estimate that takes into account both the high-level view of the project and the detailed view of its components.
In conclusion, both top-down and bottom-up estimation methods have their own strengths and weaknesses, and the best approach will depend on the specific needs of the project and the organization. A combination of these methods can provide a more comprehensive and accurate estimate, and help organizations to make informed decisions about their projects.
