2.10 Social CBA requires all impacts - social, economic, environmental, financial etc. - to be assessed relative to continuing with what would have taken place in the absence of intervention, referred to in the Green Book as Business As Usual.
2.11 The relevant costs and benefits are those for UK society overall, not just to the public sector or originating institution. They include costs and benefits to business, households, individuals and the not-for-profit sector. Assessing the costs and benefits across all affected groups matters as a relatively low-cost public sector option, such as a new regulation, may have significant costs for businesses or households.
2.12 The costs or benefits of options should be valued and monetised where possible in order to provide a common metric. This is usually done by assessing the value which reflects the best alternative use a good or service could be put to - its opportunity cost. Market prices are the usual starting point for the valuation of costs and benefits.
2.13 For some costs and benefits there may be no market price, or the market price may not fully reflect societal costs or benefits e.g. environmental values. In these cases, valuation techniques and a range of specific standard values can be used. Where it is not possible or proportionate to monetise costs and benefits they should still be recorded and presented as part of the appraisal.
2.14 Costs and benefits should be calculated over the lifetime of the intervention or asset. For many interventions, a time horizon of 10 years is suitable. Where significant assets are involved up to 60 years may be suitable e.g. buildings and infrastructure. For interventions likely to have significant costs or benefits beyond 60 years, such as nuclear waste storage, a suitable appraisal period should be agreed at the outset.