The likelihood of detecting differences between groups of sheep following deliberate infection with Ostertagia circumcincta.

An examination of variation following deliberate infection with Ostertagia circumcincta suggested that even large parasitological differences among groups have little chance of being detected unless the number of sheep in each group is quite large. Tables that give the probability for various sample sizes are presented; these tables should aid the interpretation of previously published results and may assist in the design of future experiments.