It is crucial to implement a tried and tested estimation process for software projects to succeed. Indeed, the project estimate allows to know the amount of effort for each phase of the project, to justify the staff distribution and to determine the cost of the project.

Many software projects fail because their estimate is not reliable. Failure means the team did not meet the deadline, overran the budget or did not deliver what was expected. The Standish Group details that phenomenon and adds that, in the US, more than 50% of projects overrun by 189% their budget. Also, only 16% of projects are completed in time and according to the budget. That percentage falls to 9% for large companies.

Those overspsendings are mainly due to bad estimates. Some estimation processes are more reliable than others, as for instance the parametric estimation process which is detailed in the document.