Level of uncertainty refers to the degree to which the object of study is uncertain, from the point of view of the decision maker.  A continuum of different levels of uncertainty includes:

Exposure to environmental stressors can adversely affect health. In different studies, a wide range metrics have been applied as indicators of environmental exposure. The approaches vary from relatively simple techniques, such as distance-to-road calculation, to advanced spatial and temporal modelling. This variety in exposure metrics being used complicates comparison between studies and the combination of studies in order to derive exposure-response functions.