Data-analysis in agricultural experimentation .2. Some standard contrasts

In the preceding paper in this series (Pearce, 1992) it was explained how an experimenter can ask specific questions about the treatment responses and can obtain answers to them by using contrasts of interest. Here, two standard cases are examined, one in which treatments are quantitative in nature, like the amount of fertilizer applied or the dates on which spraying takes place, and the other in which the treatment set is formed from all combinations of two or more other sets. (Such a 'factorial set' might be formed from several kinds of herbicide being used with a range of cultivations.) Finally, a non-standard example is examined in which a well considered set of treatments provided information directly relevant to the subject of enquiry. The subject is considered with some emphasis on testing, but in many instances estimation would be better.