From a public health standpoint, the selection of drugs should be based in the first instance on efficacy, safety and sufficient quality, and only then on cost. The economic standpoint differs. It uses only one criterion for the classification of all drugs-efficiency. Efficiency is the ratio of costs to efficacy (including the desired therapeutic effects and the risks inherent in any given quality). While the most effective and least expensive drugs are preferred from the twin standpoints of public health and the economy, the criterion of economic efficiency discriminates between more effective drugs that cost more and less effective drugs that cost less.