Basic Estimation Strategies

One of the essential decisions during estimation is the abstraction level on which we estimate. At one extreme, we may predict effort for a complete project. At the other extreme, we may predict effort for individual work packages or activities. Dissonance between abstraction levels on which we are able to estimate and the level on which we need estimates is a common problem of effort prediction. We may, for example, have past experiences regarding complete projects and thus be able to predict effort for complete projects; yet, in order to plan work activities, we would need effort per project activity. Two basic estimation “strategies” exist for handling this issue: bottom-up and top-down estimation.