In the worlds of business and economics, estimation methods are subject to a great deal of debate. Researchers and managers are charged with difficult tasks, such as setting cost and time boundaries, or arriving at figures that others will use for major policy decisions. Therefore, it is critical that researchers and managers have a variety of estimation methods at their disposal to help them derive reliable estimates in different types of situations.
             Delphi and top-down estimation methods are frequently used for tasks such as cost estimation, new product development and economic research. Delphi estimation involves several stakeholders and works toward building consensus on a project estimate (Wiegers, 2000). In top-down estimation, a manager or researcher may start with an aggregate estimate and then work backwards to estimate values for the various components.
             Both Delphi and top-down estimation have their weaknesses and neither is a cure-all for every estimation scenario. However, the variety of scenarios managers and researchers face in the worlds of business and economics allows both Delphi and top-down estimation, when appropriately applied, to provide reliable and actionable estimates.
             The Delphi estimation process was pioneered by the Rand Corporation in 1948 and has received considerable attention since (Wiegers, 2000). It is, put simply, estimation by consensus. In Delphi estimation, a facilitator brings together various stakeholders or experts on a project and has each of them put together an estimate of cost, time, etc. Next, the facilitator brings together the participants to have an open discussion on the reasons for the disagreements within their various estimates. Participants then prepare their individual estimates again and meet again to discuss them. This cycle continues until consensus is reached.
             There are certainly advantages to Delphi estimation. In theory, it gets buy-in from all the people who ar...