What is the proper experimental unit for long-term rodent studies? An examination of the NTP benzyl acetate study.
The National Toxicology Program (NTP) rat bioassay on benzyl acetate shows an apparent increase in acinar-cell adenomas of the pancreas in male rats [1]. The statistical significance of the apparent trend is examined using the animal, cage, or rack/shelf location as the statistical independent experimental (sampling) unit. Experimental, statistical, and empirical considerations indicate that, in this experiment, if there is a proper experimental unit, it is the shelf of animals on a rack rather than the individual animal or cage of animals. Using the shelf as the experimental unit, the apparent increase in acinar-cell adenomas is not statistically significant. There is strong evidence for pancreatic tumor rates to differ among shelves which implies that toxicologists should consider cage randomization.
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Glaxo Inc., Research Triangle Park, NC 27709.
D000236:Adenoma / Q000139:chemically induced*; D000818:Animals; D001593:Benzyl Compounds / Q000633:toxicity*; D005260:Female; D006799:Housing, Animal; D008297:Male; D010190:Pancreatic Neoplasms / Q000139:chemically induced*; D011897:Random Allocation; D051381:Rats; D011916:Rats, Inbred F344; D012107:Research Design; D013223:Statistics as Topic; D014116:Toxicology / Q000379:methods*
D001593:Benzyl Compounds; C046412:benzyl acetate