Recommendation ETI-8: Update Optimism Bias Guidance
From Edinburgh Tram Inquiry Report, published 19 September 2023.
Recommendation
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.
In brief (written by this site)
In November 2023, Màiri McAllan, Cabinet Secretary for Transport, Net Zero and Just Transition, stated to the Scottish Parliament that the administration follows detailed guidance on procurement, risk, and optimism bias enshrined in the Treasury's Green Book, the Scottish Public Finance Manual, and the Client Guide to Construction Projects (Màiri McAllan response, Nov 2023). The record holds no update since the Scottish Government's response of November 2023 (Màiri McAllan response, Nov 2023).
Sources
AI-generated summary of the record on this page, checked by a second model and automatic checks, 26 Sep 2026. The record below is the sources' own words.
Government response
Furthermore, we follow detailed Government guidance on procurement, risk and optimism bias as enshrined in the Treasury’s Green Book, the Scottish Government’s Client Guide to Construction Projects and the Scottish Public Finance Manual. Indeed, the identification and management of risk and adherence to best practice on business case production and assessment rests at the heart of project and programme delivery within Transport Scotland and the wider Government.
How this response relates to the recommendation
Site note: This paragraph follows the statement's passage on "the remaining thirteen recommendations" and is its only reference to optimism bias.
Delivery
No statement on delivery from Scottish Government has been found in the sources searched (last checked 31 January 2026). This is separate from the response above.
Responsible bodies
Themes and tags
Who has spoken
- Scottish Government
Response