(interindividual variability), the uncertainty in extrapolating animal data to the human population (interspecies uncertainty), the uncertainty in extrapolating from data obtained in a study involving less-than-lifetime exposure (extrapolating from subchronic to chronic exposure), the uncertainty in using LOAEL data rather than NOAEL data, and the uncertainty associated with extrapolation when the database is incomplete.16 A UF of 10 is considered to be a health-protective default value to be used when little is known about a particular source of variability or uncertainty or when information on a relevant health effect is lacking. As additional research becomes available, UFs change as indicated by the new information.


volume of gastrointestinal tract.


describes, in units of milligrams per hour, the maximal capacity or velocity for binding or transport, such as binding or transport of iodide by the NIS.


describes, in units of milligrams per hour per kilogram of body weight, the maximal capacity or velocity for binding or transport scaled by body weight according to the equation: Vmax (mg/hr) = [VmaxC (mg/hr per kg)][body weight (kg)]0.70.


volume of skin.



EPA (U.S. Environmental Protection Agency). 2003. Glossary of IRIS Terms. Integrated Risk Information System (IRIS). [Online]. Available http://www.epa.gov/iris/gloss8.htm [accessed April 16, 2004].


CanSIS (Canadian Soil Information System). 1996. Glossary: Caliche. Canadian Soil Information System, Canada Department of Agriculture, Ottawa. [Online]. Available: http://sis.agr.gc.ca/cansis/glossary/index.html [accessed April 16, 2004].


Colton, T. 1974. Statistics in Medicine, 1st Ed. Boston: Little, Brown and Company.


Stedman, T.L. 2000. Stedman’s Medical Dictionary, 27th Edition. Philadelphia: Lippincott Williams and Wilkins.


Rosner, B. 1995. Pp. 23-24 in Fundamentals of Biostatistics. Belmont, CA: Duxbury Press.


Altman, D.G. 1991. Practical Statistics for Medical Research. London: Chapman and Hall.


IOM (Institute of Medicine). 2000. Iodine. Pp 258-289 in Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press.

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