Update Optimism Bias Guidance
The existing Guidance on optimism bias was based on empirical data available almost two decades ago and should be revised to take into account the additional data that is now available. In particular, the reference classes should be updated to include a specific reference to light rail projects and the recommended uplifts for the different reference classes should be adjusted to reflect the additional empirical data that is now available. Thereafter the Guidance should be reviewed and revised to take account of additional data on a regular basis at intervals of not more than five years.
- No published update to optimism bias guidance incorporating light rail project data or reflecting current empirical evidence has been identified to March 2026.
How was this evidence gathered?
Response
Accepted in Part
Response
Accepted in PartThe Scottish Government stated it already operates in line with best practices but will consider updating guidance. Source: Transport Secretary Statement, 2 November 2023.
Progress Timeline
Initial status based on Scottish Government and City of Edinburgh Council responses to the Edinburgh Tram Inquiry Report (September 2023).