SAMPLE SIZE FOR EXPERIMENTS ON MILK YIELD

Graphs are presented that will permit dairy researchers to estimate the number of cows required to have 50 or 80% chance of detecting specified differences in true mean milk yield between two or more treatment groups. Relatively small experiments are shown to be almost hopelessly insensitive unless experimental errors can be reduced below levels ordinarily encountered. If an experimenter has available fewer than ten cows per treatment, estimates show he has less than a 50% chance of detecting a true mean difference in daily milk yield of 4 kg in a completely randomized experiment, 3.5 kg with a covariance analysis, 3.2 kg in a randomized block design, or 1.2 kg in a crossover trial. © 1969, American Dairy Science Association. All rights reserved.