Economic data
Optimism Bias
Project appraisers have the tendency to be over optimistic. Explicit adjustments should therefore be made to the estimates of a project's costs, benefits and duration, which should be based on data from past or similar projects, and adjusted for the unique characteristics of the project in hand.
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Optimism Bias (PDF 100KB)
This guidance provides cost and time uplift percentages for generic project categories which should be used in the absence of more robust primary data/evidence. -
CLG Guidance on Optimism bias (CLG website, opens in new window)
Link to the 'optimism bias in appraisal' section of the CLG website, where research reports and guidance notes can be found on optimism bias in contexts including regeneration projects, Decent Homes projects, and fire projects.
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