The purpose of research is to discover or change laws and theory while the purpose for evaluations is to affix a value to the process or outcome. Research is used to define a cause:effect relationship between independent and dependent variable(s). Currently, such experimental studies either are impossible to conduct in the setting of a disaster or are considered unethical. Until recently, reports of disaster responses primarily have been anecdotal and descriptive with little or no structure. They have had little value in the elimination of hazards, reduction of risks, improvement in the absorbing and/or buffering capacities, reduction in vulnerability, and or enhancement of disaster preparedness. They have served to shape our perceptions of the medical and public-health needs associated with certain events. During the last two decades, methodologies used in the social sciences gradually have been adapted to the study of disasters. Such studies have contributed greatly to our understanding of the pathophysiology of disasters and the effects of specific interventions on the affected populations or populations at risk for an event. Not all aspects of such interventions can be measured, but most can be assessed using qualitative methodologies. The importance of using both qualitative and quantitative assessments of effects is discussed.