2.4 Appraisals are often iterated a number of times before their proposals are implemented in full. Therefore the stages set out below may be repeated, and they may not always be followed sequentially. In particular, as options are developed, it will usually be important to review more than once the impact of risks, uncertainties and inherent biases. This helps to avoid spurious accuracy, and to provide a reasonable understanding of whether, in the light of changing circumstances, the proposal is likely to remain good value for money.
2.5 As the stages of an assessment progress, data must be refined to become more specific and accurate. The effort applied at each step should be proportionate to the funds involved, outcomes at stake, and the time available. Accordingly, in the early steps of identifying and appraising options, summary data only is normally required. Later on, before significant funds are committed, the confidence required must increase.