Last week I attended a meeting of members of the Latin American Initiative for Public Policy Research (ILAIPP) or Iniciativa Latinoamericana de Investigación para las Políticas Públicas, supported by the Think Tank Initiative and hosted at GRADE, in Lima. One of the inputs to the event was a presentation of a pilot to test the usefulness of the Return on Investment method for evaluating the impact of think tanks. I tried this before for a project for DFID in relation to its efforts to influence health policy in developing countries and in multilateral agencies. It was an interesting attempt but it did not yield conclusive results nor was it at all useful to know what worked and why. If anything, any lessons learned from the exercise came from the qualitative aspects of the study.