Study design

3. The question of sample size is considered in Video5. In view of the animal variation that is generally expected a sample size of 8 goats per genotype/feeding regime group is likely to be the minimum reasonable number for this study, particularly as specific recommendations are expected from the experiment. Should there be no significant interactions, however, the experiment will result in sample sizes of 24 goats for comparisons of average genotype differences on the one hand, and of average feeding regime differences on the other. The summing of one factor over another illustrates a powerful feature of factorial experiments. In this case, however, the researcher is interested in determining optimal feeding regimes for each genotype and there are likely to be significant interactions. Thus, eight goats per group are likely to be the minimum desirable sample size.