1.62 The Pre-FBC Optimism Bias Factor represents the increase in the estimated costs or the shortfall in the income or benefits of a project between OBC and FBC. A view of the level of the Pre-FBC Optimism Bias Factor seen typically can be obtained by a Procuring Authority studying changes between estimates recorded in the OBCs and FBCs of broadly similar projects previously approved, either by it or by its sponsoring Department