Optimism bias
The Green Book, Central Government Guidance On Appraisal And Evaluation, Published by HM Treasury in 2018, suggests that: ‘Optimism bias is the proven tendency for appraisers to be over-optimistic about key project parameters, including capital costs, operating costs, project duration and benefits delivery.’
Project Routemap, Setting up projects for success, Organisational Design & Development, UK Module, published by the Infrastructure and Projects Authority, defines optimism bias as: ‘The demonstrated and systematic tendency to overemphasise positive benefits and opportunities and undervalue the costs and negative risks of projects. This bias should be quantified when developing cost plans and schedules.’
Guide for Effective Benefits Management in Major Projects, published by the Infrastructure and Projects Authority in October 2017, defines optimism bias as: ‘The tendency to overestimate the probability of positive events (e.g. realisation of benefits) and underestimate the probability of negative events (e.g. risks and costs).’
[edit] Related articles on Designing Buildings Wiki
Featured articles and news
New President of ECA announced
Ruth Devine MBE becomes the 112th President of the Electrical Contractors Association.
New CIAT Professional Standards Competency Framework
Supercedes the 2019 Professional Standards Framework from 1 May 2025.
Difficult Sites: Architecture Against the Odds
Free exhibition at the RIBA Architecture Gallery until 31 May.
PPN 021: Payment Spot Checks in Public Sub-Contracts
Published following consultation and influence from ECA.
Designing Buildings reaches 20,000 articles
We take a look back at some of the stranger contributions.
Lessons learned from other industries.
The Buildings of the Malting Industry. Book review.
Conserving places with climate resilience in mind.
Combating burnout.
The 5 elements of seiri, seiton, seiso, seiketsu and shitsuke.
Shading for housing, a design guide
A look back at embedding a new culture of shading.
The Architectural Technology Awards
The AT Awards 2025 are open for entries!
ECA Blueprint for Electrification
The 'mosaic of interconnected challenges' and how to deliver the UK’s Transition to Clean Power.
Grenfell Tower Principal Contractor Award notice
Tower repair and maintenance contractor announced as demolition contractor.
Passivhaus social homes benefit from heat pump service
Sixteen new homes designed and built to achieve Passivhaus constructed in Dumfries & Galloway.
CABE Publishes Results of 2025 Building Control Survey
Concern over lack of understanding of how roles have changed since the introduction of the BSA 2022.