As a management consultant I have been confronted with impact evaluations and to put it in layman's terms I must say 1) The benefits of an intervention, in most cases, continue to accrue over a long time in future therefore CBA becomes tedious and less accurate by making too many assumptions for the future. 2) Behavioral change is indeed the most sought after goal of most the interventions and they have a snowballing effect after a certain period of inertia. It is difficult to project with any accuracy what those effects would be so it becomes like an exercise of fantasy. 3. The benefits cut across sectors. At least in the long run. Again the same problem. So, in my view a more realistic and cogent set of KPIs other than an accounting approach would be a better solution. The KPIs to be set at the beginning of a project after a baseline to benchmark against would be the nearest to accurate and acceptable.