J. Anim Sci.
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J. Anim Sci. 1973. 37:221-222.
© 1973 American Society of Animal Science
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The Responsibility of FDA to the Livestock Industry and the Consumer. V. Statistical Evaluation and Interpretation of Experimental Data1

R. J. Condon and R. P. Lehmann

Food and Drug Administration,2 Rockville, Maryland 20852

Abstract

In evaluating responses in animal productivity resulting from administration of various levels of a drug, drug levels should be treated as a continuous variable. That is, the response should be analyzed as a continuous function of the level of treatment application. Frequently, effects of continuous treatments have been evaluated by point-to-point comparisons. As an example, four levels of an antibiotic are fed to pigs and weight gains are measured. Response of level 1 is compared to level 2; response of level 2 is compared to level 3; response of level 3 is compared to level 4. Alternatively, some other scheme of level-to-level comparison may be used to evaluate weight gain responses.

Point-to-point comparisons of responses to continuous treatments have four main disadvantages: (1) there is no allowance for interpolation between levels; (2) a stepwise response is implied, which is not biologically consistent with the nature of the treatment response being evaluated; (3) statistical significance between different treatment levels is usually required for interpretation of the treatment response; and (4) the degree of statistical significance of the response between adjacent treatment levels decreases as the number of treatment levels increase over the same treatment range.

Footnotes

1 Presented as part of a Symposium, The Responsibility of FDA to the Livestock Industry and the Consumer, at the Annual Meeting of American Society of Animal Science, Blacksburg, Virginia, August 1, 1972.

2 Division of Nutritional Sciences, Bureau of Veterinary Medicine.






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