Analysis of Covariance: A Delicate Instrument

. . we would emphasize that the analysis of variance and covariance, like other statistical techniques, is not a mill which will grind out results automatically without, care or forethought on the part of the operator. It is a rather delicate instrument which can be called into play when precision is needed, but requires skill as well as enthusiasm to apply to the best advantage. The reader who roves among the literature of the subject will sometimes find elaborate analyses applied to data in order to prove something which was almost obvious from careful inspection right from the start; or he will find results stated without qualification as significant without any attempt at critical appreciation.