Experimental Designs

The first great stimulus to the development of the theory and practice of experimental design came from the agricultural research. R.A.Fisher realized that the current practice in field plot trials is failed to produce an unambiguous conclusions. This led him from about 1923 onward to examine the principles underlying scientific experimentation and to evolve new methods of design. It is not necessary to devise the procedures that would allow the drawing of valid inferences from experimental results, but these inferences has to freed as far as possible from the obscuring effect of the variability inherent in the material and the nature of the observations.  The randomization was not only needed in order to remove bias, but also for making the valid estimates of standard errors. The labour of performing experiments and the number of questions requiring investigation were as great as to make imperative methods that use most effectively the materials and effort employed and must give results of high precision. The credit for stating mostly goes to fisher and solving these problems and creating a new branch of science from which experimentation in many fields of research has benefited. Although this science of experimental design in nowadays is widely used in biology and elsewhere, the standard nomenclature retains evidence of its agricultural origin.

Some of its main important topics are:

1. Randomized blocks vs. Latin square

2. Latin square

3. Computation of trend values

4. Trends