In public health risk assessment: The qualitative or quantitative estimation of the likelihood of adverse effects that may result from exposure to specified health hazards or from the absence of beneficial influences. Risk assessment uses clinical, epidemiologic, toxicologic, environmental, and any other pertinent data. The process of determining risks to health attributable to environmental or other hazards. The process consists of four steps, as follows: 1) Hazard identification: Identifying the agent responsible for the health problem, its adverse effects, the target population, and the conditions of exposure. 2) Risk characterization: Describing the potential health effects of the hazard, quantifying dose-effect and dose-response relationships. 3) Exposure assessment: Quantifying exposure (dose) in a specified population based on measurement of emissions, environmental levels of toxic substances, biologic monitoring, etc. 4) Risk estimation: Combining risk characterization, dose-response relationships, and exposure estimates to quantify the risk level in a specific population. The end result is a qualitative and quantitative statement about the health effects expected and the proportion and number of affected people in a target population, including estimates of the uncertainties involved. The size of the exposed population must be known.