Reinhardt, V., Reinhardt, A. 2000. The lower row monkey cage: An overlooked variable in biomedical research. Journal of Applied Animal Welfare Science 3(2), 141-149.

A survey of 96 primatological articles revealed that cage location of research monkeys is usually not mentioned (98%), in spite of the fact that the environment of upper- and lower-row housed animals markedly differs in terms of light quality, light intensity and living dimension. Not accounting for these uncontrolled variables may increase variability of data and, consequently, the number of experimental animals needed to obtain statistically acceptable results. It was concluded that single-tier housing would be an important refinement of research methodology: a) by enabling all animals of a room to use the arboreal dimension of their enclosure and retreat to safe vantage points above the human predator, b) by offering all animals access to more uniform light, and c) by providing more favorable conditions for professional animal care.