Comment this: 1. Top-Down versus Bottom-Up Estimating Methods Top-down estimates begin with the 'big picture,' which is sometimes initiated from top management in the early phases of a project. The entire project is then considered, perhaps similar projects in the past (analogue estimates) with high-level calculations (ratios, function points), with the goal of reaching an overall project cost and duration estimate quickly with minimal project information required. It is appropriate for early feasibility studies on a project with high levels of uncertainty where work packages haven't yet been scoped out in more detailed work. The inaccuracy contained within it is its only significant limitation since it doesn't consider the nuances in each specific project activity. Conversely, bottom-up estimating begins with the specifics. It requires the use of the Work Breakdown Structure (WBS) to identify even the smallest work packages for a project. It also requires the specific identification by the workers themselves of the time, costs, and technical resources required for each work package. The estimates for each work package merge from the WBS to give an overall project time and cost. Though more time-consuming with a higher need for project scope definition, it is more accurate since it takes into consideration every aspect of the project, particularly where time and costs are significant factors, in fixed-price contracts, or where project plans need to be provided to clients