Animal Number Justification

In accordance with Federal Regulations, all NCI at Frederick investigators are required to consider the replacement of animal models (in vitro, computer models, etc.) to accomplish the objectives of his/her proposed research study. When it is determined that reasonable alternatives cannot replace the use of in vivo models, the NCI at Frederick Animal Care and Use Committee (ACUC) is responsible for ensuring that investigators have adequately assessed their study requirements to ensure that the number of animals are appropriate to accomplish the proposed research objectives. Specifically, the investigator must ensure that he/she is using the minimum number of animals necessary (avoid overpowering the study) while using an adequate number of animals (avoid underpowering the study) to provide data that is relevant to fulfill his/her experimental objectives without unnecessary repetition of the study (please refer to the Determination of Sample Sizes document provided by the DMS Statistical Consultation Group for additional guidance). The following information is provided to assist investigators with this task:

Animal Care and Use Committee Guidance

The ACUC provides a general guidance for three categories of studies (experimental design, tissue/organ/fluid harvests for in vitro studies, and biological reagent/cell production) to assist investigators with the approach that should be utilized when providing an animal number justification.

Animal Numbers for Research Use Calculator

In an effort to assist investigators with determining the number of animals that are necessary to support their breeding studies, the Laboratory Animal Sciences Program has designed this calculator for your use.

Historical and/or Reference Data

Investigators are permitted to utilize historical and/or reference data to support the animal number justification provided to the NCI at Frederick Animal Care and Use Committee. It is imperative that the investigator outlines his/her justification by including the specific historical data analysis and/or appending published reference documents.

Determination of Sample Sizes

The Data Management Services (DMS) Statistical Consultation Group provides information on how sample sizes are determined. The goal of this document is to make clear the issues associated with sample size determination and why investigators often need help with this process. The ACUC encourages investigators to contact the DMS Statistical Consulting Group (301-846-5101) in advance of Animal Study Proposal submission for assistance with his/her animal number justification.

Design and Statistical Methods in Studies Using Animal Models of Development

This article by Michael F.W. Festing outlines the requirements for a well-designed experiment to include information for determining suitable research strategies, choosing appropriate models, sample sizes, and statistical analysis. Reprinted with permission from ILAR Journal, (Volume 47, Number 1), Institute for Laboratory Animal Research, The Keck Center of the National Academies, 500 Fifth Street NW, Washington DC 20001 (

Power Calculators

These calculators, found on the UCLA Department of Statistics website, were written in PHP by Arno Ouwehand, using the DSTPLAN distribution by Barry Brown et al. These calculators extend the functionality of the old Xlisp-Stat based Power Calculator by not only computing the power for given sample size, or sample size for given power, but will also compute the other available items when specified.