Step Five: Prepare Baseline Estimate
Budget and schedule are derived from estimates, so if an estimate is not accurate, the resulting schedules and budgets are likely to be inaccurate also. Given the importance of the estimation task, developers who want to improve their software estimation skills should understand and embrace some basic practices. First, trained, experienced, and skilled people should be assigned to size the software and prepare the estimates. Second, it is critically important that they be given the proper technology and tools. And third, the project manager must define and implement a mature, documented, and repeatable estimation process.
To prepare the baseline estimate there are various approaches that can be used, including guessing (which is not recommended), using existing productivity data exclusively, the bottom-up approach, expert judgment, and cost models.
Software Productivity Laws
These laws of software productivity help explain the dynamics of an engineering development project, and they illustrate some of the reasons that just using productivity to estimate is inadequate.
Law 1 - Smaller teams are more efficient. The smaller the team, the higher the productivity of each individual person.
Law 2 - Some schedule compression can be bought. Adding people to a project, to a point, decreases the time and increases the cost as larger teams work together.
Law 3 - Every project has a minimum time. There is an incremental person who consumes more energy than he or she produces. Team size beyond this point decreases productivity and increases time. (Law 3 is also known as Brooks’ law.)
