An empirical study of maintenance and development estimation accuracy

We analyzed data from 145 maintenance and development projects managed by a single outsourcing company, including effort and duration estimates, effort and duration actuals, and function points counts. The estimates were made as part of the company’s standard project estimating process that involved producing two or more estimates for each project and selecting one estimate to be the basis of client-agreed budgets. We found that effort estimates chosen as a basis for project budgets were, in general, reasonably good, with 63% of the estimates being within 25% of the actual value, and an average absolute error of 0.26. These estimates were significantly better than regression estimates based on adjusted function points, although the function point models were based on a homogeneous subset of the full data set, and we allowed for the fact that the model parameters changed over time. Furthermore, there was little evidence that the accuracy of the selected estimates was due to their becoming the target values for the project managers.