the usefulness of specified inputs (costs) to produce specified outputs (benefits) —note 1. in measuring cost effectiveness, some outputs, including environmental, economic, or social impacts, are not assigned monetary values but are achieved at specified levels in the least-cost manner —note 2. cost effectiveness is usually measured using present net value, although use of benefit-cost ratios and rates-of-return may be appropriate —note 3. the cost effectiveness ratio is the ratio of costs (generally at present value and generally measured as social costs) to a standard measure of performance, which may be related to pollution abatement, mitigation, or some other policy standard This definition last updated 07/28/2008