Estimate The Project Work Before Gathering Detailed Requirements

Estimate the Project Work Before Gathering Detailed Requirements
There is concern from many project managers that they are expected to present a detailed estimate of the project work when thecharter and schedule are created. However, the detailed requirements have not been gathered yet. So how are you supposed to estimate the work without having captured the detailed requirements? It seems likea valid question. Yet, when you talk about gathering detailed requirements, you are usually talking about the Analysts Phase of a project lifecycle, not the up-front project management work ofdefining and planning the project. 
Your first thought might be that perhaps you should have the detailed requirements before you commit to an estimate for the work. However, is that really practical?Let’s say you have a process improvement project. The project might last six months and the requirements gathering process might last six weeks (or more) of that overall timeframe. So, should you reallyhold off on the project estimates until the requirements are gathered and approved? If so, the project might be one-third complete before you are validating the overall project costs and deadline. If theproject does not make sense from a cost-benefit perspective, you might have already spent a significant amount of money. This is much too late, and it is the reason most project managementmethodologies don’t include the gathering of detailed business requirements.
Also if you use this same argument, you might say that you still are not confident to estimate the work without first doing thedesign, and then you are not confident to estimate the work until you have the construction work done, etc. You see that this same logic can be taken to an extreme. 
The following three approaches willallow you to estimate the work before you have gathered the detailed business requirements. (These assume that you are gathering requirements as the first step of project execution. This is also...