The measurement and valuation of clinical effects is a significant component of economic evaluation. Decision makers are commonly interested in how a particular health intervention works in everyday practice; therefore, the resulting outcome under this circumstance is called the effectiveness. Clinical effects usually measure final intended effects of a proposed health technology in terms of the ultimate change in health state brought about by the technology. The systematic review and meta-analysis of high quality RCTs is the most favorable method to synthesize evidence because they are disciplined and transparent methods. The present chapter focuses on how to make a valid measure of clinical effects for use in cost-effectiveness analysis and how clinical effect is to be appropriately defined and measured.