2 Analogous estimating. Analogous estimating, also called top-down estimating,means using the actual duration of a previous, similar activity as the basis for estimating the duration of a future activity. It is frequently used to estimate project duration when there is a limited amount of detailed information about the project(e.g., in the early phases). Analogous estimating is a form of expert judgment (described in Section 6.3.2.1).
Analogous estimating is most reliable when (a) the previous activities are similarin fact and not just in appearance, and (b) the individuals preparing the estimates have the needed expertise.