Estimating by analogy

The use of analogy is also called case-based reasoning. The estimator seeks out projects that have been completed (source cases) and that have similar characteristics to the new project (the target case). The effort that has been recorded for the matching source case can then be used as a base estimate for the target. The estimator should then try to identify any differences between the target and the source and make adjustments to the base estimate for the new project.

Iliis might be a good approach where you have information about some previous projects but not enough to draw generalized conclusions about what variables might make good size parameters.

A problem here is how you actually identify the similarities and differences between the different systems. Attempts have been made to automate this process. One software application that has been developed to do this is ANGEL. This identifies the source case that is nearest the target by measuring the Euclidean distance between cases. The source case that is at the shortest Euclidean distance from the target is deemed to be the closest match. The Euclidean distance is calculated:

distance = square-root of ((target_parameter, - source_parameterx)' +

Example 5.1 Say that the cases are being matched on the basis of two parameters, the number of inputs to and the number of outputs from the system to be built. The new project is known to require 7 inputs and 15 outputs. One of the past cases. Project A. has 8 inputs and 17 outputs. The Euclidean distance between the source and the target is therefore the square-root of ((7-8)'+( I7-I5)2). that is 2.24.

Exercise 5.4

Project B has 5 inputs and 10 outputs. What would be the Euclidean distance between this project and the target new project being considered above? Is l*roject B a belter analogy with the target than Project A?

The above explanation is simply to give an idea of how Euclidcan distance might be calculated. The ANGEL package uses rather more sophisticated algorithms based on this principle.

Project Management Made Easy

Project Management Made Easy

What you need to know about… Project Management Made Easy! Project management consists of more than just a large building project and can encompass small projects as well. No matter what the size of your project, you need to have some sort of project management. How you manage your project has everything to do with its outcome.

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