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Title: THE POWER OF TESTS FOR BIOEQUIVALENCE IN FEED EXPERIMENTS WITH POULTRY

Author
item Roush, William
item TOZER, P - PENN STATE UNIV, PA

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2004
Publication Date: 10/15/2004
Citation: Roush, W.B., Tozer, P.R. 2004. The power of tests for bioequivalence in feed experiments with poultry. Journal of Animal Science. 82(E. Suppl):E110-E118.

Interpretive Summary: Several studies have compared the feeding genetically modified grains and conventional grains to poultry. The general conclusion has been that there are no differences in the biological performance of the birds. However, the question has been asked whether enough samples were taken to detect treatment differences. Tests for statistical power can be used to determine the number of samples needed to detect treatment differences. In the current study, examination was made of experiments published in the literature to see if enough samples were taken to detect differences between birds fed genetically modified grains and birds feed conventional grains. The results of the literature survey showed that, in general, the sample sizes were insufficient to detect small differences between birds fed genetically modified and conventional grains. These results indicate that care needs to be taken to insure sufficient samples are taken when designing experiments for testing new grains for poultry. Suggestions were made to improve the statistical design of grain studies.

Technical Abstract: Several studies have compared the feeding 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, in fact, false and should be rejected. The complement of statistical power is the Type II error (ß). That is, accepting the null hypothesis that there is no difference in treatments when, in fact, there is one. A priori power analysis can indicate the probability at which the sampling regime 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, examination was made of the power of tests for experiments published in the literature where significant and non-significant differences were reported between control birds and birds fed new feed grains. 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 in feeding experiments involving either non-GM grains were fed to poultry, or 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 in feeding poultry.