In order to measure the average optimism bias levels for similar projects, the projects were initially divided into sectors (i.e. health, transport, prisons, power stations, defence, information technology, PFI and others). However, initial analyses indicated similarities across the sectors (e.g. typical prison projects recorded similar levels of optimism bias as typical hospital projects). Consequently, the projects studied were grouped according to project type as this was deemed more meaningful. The categories for project type are described below:
1. Standard buildings projects: Projects that involve the construction of buildings not requiring special design considerations i.e. most accommodation projects (offices, living accommodation, general hospitals, prisons, and airport terminal buildings) e.g. Woodhill Prison
2. Non-standard buildings projects: Projects that involve the construction of buildings requiring special design considerations due to space constraints, complicated site characteristics, specialist innovative buildings or unusual output specifications i.e. specialist/innovative buildings (specialist hospitals, innovative prisons, specialist barrack accommodation and other unique buildings or refurbishment projects) e.g. Chelsea and Westminster Hospital, which was located on a brown-field site, with restricted area and access and as a result required special design considerations
3. Standard civil engineering projects: Projects that involve the construction of facilities, in addition to buildings, not requiring special design considerations i.e. most new roads and some utility projects e.g. Yorkshire Link M1-A1
4. Non-standard civil engineering projects: Projects that involve the construction of facilities, in addition to buildings, requiring special design considerations due to space constraints or unusual output specifications i.e. innovative rail, road, utility projects and upgrade and extension projects e.g. Jubilee Line Extension, which had to be constructed with innovative tunnelling methods in proximity to a landmark building (e.g. the Palace of Westminster)
5. Equipment & development projects: Projects that are concerned with the provision of equipment and/or development of software and systems (i.e. manufactured equipment, Information and Communication Technology (ICT) development projects) or leading edge projects e.g. MoD Defence Fixed Telecommunications Service (DFTS)
6. Outsourcing projects: Projects that are concerned with the provision of hard and soft facilities management services i.e. ICT services, facilities management or maintenance projects e.g. PRIME