A5.12 Risk should be quantified and costed in a proportionate way. Where relevant this should include the costs of mitigation and the expected costs if risks materialise. The extent to which risk is identified allows the initial estimates of optimism bias to be reduced (as set out in Step 4 above). As an appraisal develops the cost of risk should be estimated and included in the estimated costs of an intervention. This is not a mechanistic relationship and will be a judgement of the extent to which relevant risks have been identified and quantified. There are various techniques set out in the next sections that can be used to calculate risk costs.