World Association for the Advancement of Veterinary Parasitology (W.A.A.V.P.) Guidelines for evaluating the efficacy of anthelmintics in swine

Use of arithmetic and geometric means in the calculation of anthelmintic efficacy

“…In a number of publications (Powers and others 1982, Duwell and others 1986, Duncan and others 1988), the type of mean to be used in these calculations is not specified but it appears to be a commonly accepted convention that the term ‘mean’ usually refers to the arithmetic mean (Sokal and Rohlf 1969, Langley 1971, Zar 1984). Nevertheless, in the revised waavp guidelines referred to earlier (Wood and others 1995), it was stated that for calculations of percentage efficacy, ‘The geometric mean should be used as it more accurately represents the distribution of nematode populations within a group of animals and would give a more accurate indication of the degree of efficacy of a product’.…”