Project Management for IT-Related Projects

6.5 A parametric approach

The base estimate created when using a top-down approach can be derived in a number of ways. In estimating the costs of rebuilding a house, a parametric method was used. This means that the estimate was based on certain variables or parameters (for example, the number of storeys in the house and the number of bedrooms). These parameters can be said to ‘drive’ the size of the house to be built: you would expect a house with three storeys and five bedrooms to be physically bigger than a bungalow with only two bedrooms. These parameters are therefore sometimes called size drivers. You would also expect the three-storey building to need more work, or effort, to build than the bungalow. These parameters are also sometimes ...