In order to translate the evidence from past projects into guidance to allow for optimism in current and future public procurement, it is necessary to understand the changes in both the external environment and normal procurement practice (e.g. preparation of business case) that have occurred since the projects studied were completed.
On the basis of the sample of projects analysed, this section identifies key changes and trends and comments on the relative importance of residual influences on optimism bias. This section also identifies sources of optimism bias that either lie outside the control of the project manager or are within the remit of project procurement.