Studies have shown that optimism bias is caused by a failure to identify and effectively manage project risks. The Mott MacDonald study identified five common project risk groups containing a number of project risk areas recorded as causing costs and time overruns, and benefits shortfalls. Table 5 in Appendix E contains a breakdown of these project risk groups into project risk areas. Note that the project risk areas identified in Table 5 should be managed for all projects types even if they have not been specifically identified as contributing towards optimism bias levels.