3.13 The quantitative assessment at the investment programme stage will inevitably be conducted using only high-level estimates supported by evidence taken from past procurements, since all input assumptions should be predicated as far as possible upon evidence from past experience and projections. This approach has been adopted in part to discourage overly complex modelling and promote simplicity, as well as to reflect the inherent uncertainties at this point in the process. However, the quantitative assessment will develop further as more detailed information feeds back from previous programmes and constituent projects.
3.14 In completing their programme-based assessments, departments should have regard to the level of homogeneity of those projects that are likely to fall within each programme. Where the variety of projects within an investment programme is substantial, departments will need to ensure that the specific characteristics of each project are tested robustly at Stage 2. Given the uncertainty that a high level of variety in projects in a programme at Stage 1 creates, it is also important to make sure this is reflected in the stage 1 quantitative assessment. The programme assessment should consider scenarios beyond just the "typical" project, and look at the potential volatility of the programme.
3.15 For certain projects it may be particularly hard to gather relevant data inputs. In this case other information should be sought to justify the inputs into the model and steps taken to remedy this gap for future procurements (the Quantitative User Guide addresses possible ways this can be achieved).