Another risk is that there is a systematic tendency for both public and private sector project appraisers to be overly optimistic (e.g. the decision for the wider roll-out of a programme is based on the findings of a well-resourced pilot, which cannot be mirrored on a larger scale due to budgetary constraints or unanticipated negative side-effects). This contrasts with economic theory for a labour market in equilibrium, in which the social value of additional work at the margin is zero, because additional output of value to other members of society is offset by the loss of leisure of value to the worker. Conducting a full cost-benefit analysis (cont.)