Information Resources for Institutional Animal Care and Use Committees 1985-1999 *************************

Statistics and Animal Numbers


Baker, D.G. (1998). Natural pathogens of laboratory mice, rats, and rabbits and their effects on research. Clinical Microbiology Review 11(2): 231-266.
NAL call number: QR67.C54
Abstract: Laboratory mice, rats, and rabbits may harbor a variety of viral, bacterial, parasitic, and fungal agents. Frequently, these organisms cause no overt signs of disease. However, many of the natural pathogens of these laboratory animals may alter host physiology, rendering the host unsuitable for many experimental uses. While the number and prevalence of these pathogens have declined considerably, many still turn up in laboratory animals and represent unwanted variables in research. Investigators using mice, rats, and rabbits in biomedical experimentation should be aware of the profound effects that many of these agents can have on research.
Descriptors: bacterial infections, parasitic diseases, rodent diseases, virus diseases, microbiology, mice, rabbits, rats, reproducibility of results, epidemiology, immunology, parasitology, virology.

Crouse, D.A., Mann, M.D., and E.D. Prentice (1995). The logical determination of "n" in animal experimentation. In "Current Issues and New Frontiers in Animal Research, K.A.L. Bayne, M. Greene, and E.D. Prentice, eds., Greenbelt, Maryland: Scientists Center for Animal Welfare, pp. 19-23.
NAL call number: HV4913.C87 1995
Descriptors: review of basic elements that significantly impact animal use, review of statistical parameters which should be considered in the design of a typical research protocol, review by IACUC, Type I vs Type II error, level of significance.

Erb, H. (1996). A non-statistical approach for calculating the optimum number of animals needed in research. Lab Animal 25(3): 45-49.
NAL call number: QL55.A1L33
Descriptors: elements of sample size calculation, assessment of the kind of data, descriptive vs. comparative analysis, common sample size mistakes, methods to decrease sample size.

Festing, M.F.W. (1995). Variation and experimental design. Scientist Center for Animal Welfare Newsletter 18(3): 3-9.
NAL call number: QL55.N48
Descriptors: minimizing animal numbers, variability, laboratory animals, quality control, statistical analysis, experimental design, understanding variation in experimental results.

Festing, M.F.W. (1994). Reduction of animal use-experimental design and quality of experiments. Laboratory Animals 28(3): 212-221.
NAL call number: QL55.A1L31
Descriptors: variability, animal numbers, statistical analysis, understanding statistics.

Festing, M.F.W. (1992). The scope for improving the design of laboratory animal experiments. Laboratory Animals 26(4): 256-267.
NAL call number: QL55.A1L31
Descriptors: principles of experimental design, no built in bias, precision, variability, control of variability, ability to detect differences, practical considerations versus theoretical statistical considerations, simplicity, experimental error, completely randomized single-factor design, randomized block design, increase in efficiency from randomized block designs, factorial arrangement of treatments, review.

Geller, N.L. (1983). Statistical strategies for animal conservation. Annals of the New York Academy of Sciences 406:20-29.
NAL call number: 500 N484
Descriptors: randomization, confounding factors, sample size and power, analysis, group sequential designs, historical controls, serial sacrifice, carcinogenesis, bioassays, teratogenesis, experimental design, animal numbers, alternatives.

Khamis, H.J. (1997). Statistics and the issue of animal numbers in research. Contemporary Topic in Laboratory Animal Science 36(2): 54-59.
NAL call number: SF405.A23
Descriptors: unified approach to determining animal numbers, methods to determine and justify animal numbers, 3-step approach, pilot study or inferential study, determining minimum numbers necessary to achieve research goals, justifying animal numbers, experimental design, 3R's, examples.

Mann, M.D., Crouse, D.A., and Prentice, E.D. (1991). Appropriate animal numbers in biomedical research in light of animal welfare considerations. Laboratory Animal Science 41(1): 6-14.
NAL call number: 410.9 P94
Descriptors: statistics, sample size, variability, nonstatistical factors, ethics, economics, effect size, experimental design.

McCance, I. (1995). Assessment of statistical procedures used in papers in the Australian Veterinary Journal. Australian Veterinary Journal 72(9): 322-328.
NAL call number: 41.8 AU72
Abstract: One hundred and thirty-three papers (80 Original Articles and 53 Short Contributions) of 279 papers in 23 consecutive issues of the Australian Veterinary Journal were examined for their statistical content. Only 38 (29%) would have been acceptable to a statistical referee without revision, revision would have been indicated in 88 (66%), and the remaining 7 (5%) had major flaws. Weaknesses in design were found in 40 (30%), chiefly in respect to randomisation and to the size of the experiment. Deficiencies in analysis in 60 (45%) were in methods, application and calculation, and in the failure to use appropriate methods for multiple comparisons and repeated measures. Problems were detected in presentation in 44 (33%) of papers, with insufficient information about the data or its statistical analysis and presentation of statistics (appropriate missing or inappropriate shown) the main problems. Conclusions were considered to be inconsistent with the analysis in 35 (26%) of papers, due mainly to their interpretation of the results of significance testing. It is suggested that statistical refereeing, the publication of statistical guidelines for authors and statistical advice to Animal Experimentation Ethics Committees could all play a part in achieving improvement.
Descriptors: analysis of variance, standards, random allocation, research design , statistics reproducibility of results.

Morton, D.B. (1998). The importance of nonstatistical design in refining experiments. ANZCCART News 11(2-insert):1-11. Available at
NAL call number: SF405.5.A3
Descriptors: alternatives, refinement, use of anesthetics and analgesics, importance of skilled and competent investigators, statistical advice, limitations of scientific evidence, extrapolation and animal numbers, pilot studies, dose sighting and control groups, adverse effects causing pain and distress, humane endpoints, score sheets, recognition and assessment of pain and distress.

Orlans, F.B. (1986). Ideas for experimental design of experiments involving animals. Laboratory Animal Science 36(5): 557.
NAL call number: 410.9 P94
Descriptors: design of experiments, procedures, review process.

Ruxton, G.D. (1998). Experimental design: minimizing suffering may not always mean minimizing number of subjects. Animal Behaviour 56(2): 511-512.
NAL call number: 410 B77
Descriptors: experimental design, laboratory animals, animal numbers, animal welfare.

Straughan, D.W. (1995). The EU target for a 50% reduction in use of experimental animals by the year 2000--what does it mean? Alternatives to Laboratory Animals: ATLA 23(2): 262-263.
NAL call number: Z7994.L3A5
Descriptors: animal experiments, animal testing alternatives, animal welfare, European Union regulations.

Weigler, B.J. (1995). Justifying the number of animals in IACUC proposals. Contemporary Topics in Laboratory Animal Science 34 (3):47-50.
NAL call number: SF405.5.A23
Descriptors: laboratory animals, usage, committees, regulations, bioethics, experimental design, statistics, reviews.

Whary, M.T., D.D. Carey, and F.G. Ferguson (1998). Reduction in animal numbers required for antisera production using the subcutaneous chamber technique in rabbits. Laboratory animals 32(1): 46-54.
NAL call number: QL55.A1L3
Abstract: The purpose of this study was to determine if the subcutaneous chamber technique would reduce the number of rabbits required for antisera production by enabling serial use of individual animals for multiple antigens. Rabbits were assigned to immunization protocols against two antigens in series that involved combinations of chamber implantation, Freund's adjuvant and injection of antigen either by the subcutaneous route or by direct inoculation into the chamber. Results indicate the systemic immune response to both antigens achieved similar magnitude and duration by use of either Freund's adjuvant or direct inoculation of antigen into the chamber, suggesting that chamber use may be able to replace use of Complet e Freund's adjuvant for many antigens. Rabbits re-used for a second antigen were equally successful in production of significant titres in both serum and chamber fluid without evidence of either a significant inflammatory response due to the chronic presence of the implant or a decrease in the yield of antisera harvested from the chamber. These results support the advantages of chamber use as reported by others and demonstrate that the chamber technique can significantly extend the productive life of an individual animal that would otherwise be euthanized following a single use in antisera production.
Descriptors: rabbits, immune serum, biological production, antigens, antibody formation, yields, hemocyanins, adjuvants, cholera, bacterial toxins, containers, implantation, animal welfare, alternatives.

Useful World Wide Web Sites

Guidelines for Determination and Justification of Animal Numbers
Topics included in this site provided by the University of California at Irvine are: overview, basis, study design, pilot studies, inclusiveness, alternative methods, inbred animals, repetition of experiments, modification of approved animal number, and references.

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Last updated March 15, 2005