By experimental design, we mean a plan and used to collect the data relevant to the problems understudy in such a way as to provide a basis for valid and objective inference about a state problem. The plan he usually consists of the selection of treatments whose effects are to be studied, the specification of the experimental layouts, the assignments of treatments to the experimental units and the calculation of observations for analysis. all these steps are accomplished before any experiment is performed.
an experiment is planned to
The following considerations go into the planning of an experiment.
The answers to these questions enable the experiment to State his hypothesis precisely and to plan this experimental procedure in a more these are two types of designs systematic and random designs; Butt the analysis of variance techniques are suitable to randomize designs only. the basic randomized designs are
which we discussed in the sections that follow
Basic principles of experimental designs:
The basic principles of experimental designs are randomization, Replication and local control.
these principals make a valid test of significance possible. each of them is described briefly in the following subsections.
The first principle of an experimental design is randomization, which is a random process of assigning treatments to the experimental units. the random process implies that every possible allotment of treatments has the same probability. an experimental unit is the smallest division of the experimental material and the treatment means an experimental condition whose effect is to be measured and compared. the purpose of randomization is to remove bias and other sources of extraneous variation, which are not controllable. another advantageous of randomization is there to be assigned and random to the experimental units. randomization is usually done by drawing a numbered card from a well-shuffled pack of cards or by drawing numbers balls framer well-shaken container or by using a table of random numbers.
the second principal of an experimental design is republication which is and repetition of the basic experiment. in other words, it is and complete run from all the treatments to be tested in the experiment. in all experiments, some variation is introduced because of all the fact that experimental units such as individuals are plots of land in agriculture experiments, cannot be physically identical. This type of variation can be removed by using a number of experimental units. We, therefore, performed experimental more than once that is We repeat the basic experiment. an individual’s reputation is called the replicate. the number, the shape and the size of replicates depend upon the nature of the experimental material. Replication is used
It has been observed at all extraneous sources of variation or not removed by randomization and republication. this necessity a refinement is the experimental technique.
in other words, we need to choose a design in such a manner that all experience sources of variation or brought under control. for this purpose, we make use of local control, or term referring to the amount of balancing, blocking and grouping of the experimental units. Balancing means that the treatments should be designed for experimental units in such a way that the result is a balanced arrangement of the treatments. blocking means that like experimental units should be collected together to form of Relativity homogeneous group. a block is also a replicate. the main purpose of the principle of local control is to increase the efficiency of experimental design by decreasing the experimental errors. the point to remember here is that the term local control should not be confused with world control. The word control in experimental design is used for a treatment which does not receive any treatment but we need to find cut the effectiveness of other treatment through comparison.