Block Size and Orientation, and Allowance for Positional Effects, in Field Experiments

Abstract

SUMMARY: A random sample of 13 uniformity trials was examined in terms of sensitivity to choice of block size and orientation. Five trials were classified as insensitive and eight as sensitive. Trials insensitive to blocking choices showed little variation in experimental error for various sizes, shapes and orientations of blocks, but those sensitive to blocking choices showed considerable, sometimes drastic, effects of such choices. There was often an objectionable degree of inflation of experimental error due to large or improperly oriented blocks. It is proposed that the routine analysis of field experiments based on block designs be modified to reveal cases in which ineffective blocks have been used on sensitive sites.