Standard Article

Litter Effect

Environmental Health

  1. Lawrence L. Kupper

Published Online: 15 SEP 2006

DOI: 10.1002/9780470057339.val014

Encyclopedia of Environmetrics

Encyclopedia of Environmetrics

How to Cite

Kupper, L. L. 2006. Litter Effect. Encyclopedia of Environmetrics. 3.

Author Information

  1. University of North Carolina, NC, USA

Publication History

  1. Published Online: 15 SEP 2006


It has long been recognized that humans exposed to certain drugs, chemicals, and other environmental hazards may be at increased risk of various health problems. Exposure-related, adverse, heritable, human health outcomes currently receiving increased attention by public health professionals are fertility and pregnancy complications, birth defects, and developmental abnormalities. Well-conducted environmental epidemiology studies on human populations would provide the most relevant data for quantifying relationships between exposure levels and adverse pregnancy- related outcomes. However, useful information from observational data on humans is often limited in both quantity and quality. So, despite the obvious species-to-species extrapolation problem, controlled laboratory experiments on rodents are commonly conducted to provide developmental toxicology data. This article focuses specifically on developmental toxicology studies, where pregnant rodents are exposed to a suspected harmful agent during the period of major fetal organogenesis and structural development. It is well known that an inherent characteristic of data from such rodent teratology studies is the so-called litter effect, i.e. the tendency for littermates all to respond in the same way to stimuli, unlike animals from different litters. Litter effects seem to be present in almost all developmental toxicology studies, and data analyses that do not appropriately account for these litter effects can lead to erroneous statistical inferences.