The power of tests for bioequivalence in feed experiments with poultry

ABSTRACT Several studies have compared the feeding of genetically modified (GM) grains and conventional grains to poultry. The general conclusion has been that there were no significant differences detected in the biological performance of the birds (i.e., the grains were bioequivalent). However, the question has been posed whether the experimental designs used in the studies had sufficient statistical power to detect treatment differences. The power of tests can be used to determine the ability of an experimental design to detect treatment differences. The definition of statistical power is the probability of rejecting the null hypothesis when it is false and should be rejected. The complement of statistical power is the Type II error (β). That is, accepting the null hypothesis that there is no difference in treatments when there is one. A priori power analysis can indicate the probability at which the sampling regimen or experiment can actually detect an effect if a difference exists. Post hoc power analysis indicates the sufficiency or the sample size needed for an experiment that has already been conducted. In the current study, the power of tests for experiments published in the literature where significant and nonsignificant differences were reported between control birds and birds fed new feed grains was examined. With some exceptions, the power of tests is rarely formally considered or mentioned in poultry research. The results of the survey of the literature showed, in general, low power of statistical tests for feeding experiments involving non-GM grains or in those cases when GM and non-GM grains were compared in poultry feeding experiments. These results suggest that care needs to be taken when designing experiments for bioequivalence of grains fed to poultry.

Key Words: Bioequivalence, Genetically Modified Grains, Poultry, Power Tests

© 2004, by the American Society of Animal Science. All rights reserved.

J. Anim. Sci. 2004. 82(E. Suppl.):E110-E118

Implications

With regard to safety (perceived or otherwise) and in an effort to preserve the credibility of the research, it is important that careful consideration be given to the experimental design for the detection of differences or lack of differences. With this in mind, Buhl-Mortensen (1996) pointed out that the awareness of how methods affect results in science is crucial if we want to appraise objectively what an investigation does or does not say about the actual extent of a given risk and will help to keep science as objective as possible. Accordingly, power analysis of experimental designs for planned research is encouraged to accomplish meaningful bioequivalent feed studies for poultry.