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Power of test considerations for beef cattle experiments: A review^1,2

C. R. Richardson^*,3, G. A. Nunnery^*, D. B. Wester, N. A. Cole and M. L. Galyean^*

^* Departments of Animal and Food Sciences and and Range, Wildlife, and Fisheries Management, Texas Tech University, Lubbock 79409 and and ARS,USDA, Bushland, TX 79012

³ Correspondence: Box 42141 (phone: 806-742-2516; fax: 806-742-4003; E-mail: reed.richardson{at}ttu.edu).

The use of power tests in the planning and design of beef cattle experiments provides critical information on sample sizes necessary to detect treatment differences at a predetermined significance () level. Retrospective power analysis provides additional information about previous experiments that may be helpful in designing subsequent investigations. However, in retrospective power analyses, power is inversely related to observed significance level. Benefits of prospective and retrospective power analyses in beef cattle experiments are similar to those for other species; however, because of differences in the methods and conditions involved, considerations for the use of power test procedures are specific for beef cattle research. Retrospective power analyses were conducted on 78 published experiments and on two unpublished experiments. Experiments were compiled into categories that represented group (or pen) feeding, individual feeding, and metabolism studies. Estimated power in pen feeding experiments using randomized block designs (RBD, n = 30) was less than 0.80 for ADG and feed efficiency (FE), but not different from 0.80 for completely random designs (CRD, n = 4). Furthermore, estimated power was less for ADG than for FE in both design types. For individual feeding experiments using RBD (n = 4), power was not different from 0.80 for either ADG or FE; however, for CRD (n = 18), power was less than 0.80 for both ADG and FE. Power was similar for ADG and FE for both RBD and CRD in individual feeding experiments. In metabolism experiments, estimated power for nitrogen retention was less than 0.80 for Latin square designs (n = 20) but not for CRD (n = 4). Comparisons of power between experimental design types were likely influenced by the number of experiments involved. These results indicate that retrospective power in beef cattle experiments is affected by design type, and response variable measured.

Key Words: Beef Cattle • Experimental Design • Statistics