Precision and accuracy in estimating

The difference between precision and accuracy has always been important to engineers and it is vital to understand too in the context of estimating for software projects. One approach to estimating a project is to create a detailed work breakdown structure and estimate each task, say in person-hours. A friend told me recently she had consulted on a project which had estimated its size as 135,213 person-hours! The precision in this case is 6 significant figures. As to the accuracy however, previous projects had errors or between 10 and 200%. The precision actually gets in the way of understanding the estimate, particularly as crucial business decisions involving significant proportions of a company's revenue may be based on such numbers. While three-point estimating (3pe) provides one way of capturing risk estimates along with the estimate themselves, the main contribution of agile methods in this area is the tight feedback loop from measured velocity timebox by timebox. Check out some of the links below to see how xProcess supports these concepts.