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
OpenUSD possibilities: Look before you leap
Being ready for the OpenUSD solutions set to transform architecture and design.
Global Asbestos Awareness Week 2025
Highlighting the continuing threat to trades persons.
Retrofit of Buildings, a CIOB Technical Publication
Now available in Arabic and Chinese aswell as English.
The context, schemes, standards, roles and relevance of the Building Safety Act.
Retrofit 25 – What's Stopping Us?
Exhibition Opens at The Building Centre.
Types of work to existing buildings
A simple circular economy wiki breakdown with further links.
A threat to the creativity that makes London special.
How can digital twins boost profitability within construction?
The smart construction dashboard, as-built data and site changes forming an accurate digital twin.
Unlocking surplus public defence land and more to speed up the delivery of housing.
The Planning and Infrastructure Bill
An outline of the bill with a mix of reactions on potential impacts from IHBC, CIEEM, CIC, ACE and EIC.
Farnborough College Unveils its Half-house for Sustainable Construction Training.
Spring Statement 2025 with reactions from industry
Confirming previously announced funding, and welfare changes amid adjusted growth forecast.
Scottish Government responds to Grenfell report
As fund for unsafe cladding assessments is launched.
CLC and BSR process map for HRB approvals
One of the initial outputs of their weekly BSR meetings.
Building Safety Levy technical consultation response
Details of the planned levy now due in 2026.
Great British Energy install solar on school and NHS sites
200 schools and 200 NHS sites to get solar systems, as first project of the newly formed government initiative.
600 million for 60,000 more skilled construction workers
Announced by Treasury ahead of the Spring Statement.