A treatment
is something that a researcher administers to experimental units, and its
effect is to be investigated on the dependent variable (variable of interest).
Example:
The researcher wants to investigate the effect of three fertilisers on the
growth of vegetables.
Experimental
Material
The material on which treatments are to be tested. It
may land, machinery, etc. In the above
example, the three varieties of wheat seed can be tested to assign a plot of land.
Experimental Unit
The smallest piece of experimental material to which a
single treatment is assigned.
Design of Experiment
A DOE is a systematic approach to the preparation, execution, and analysis of an experiment.
The aim of DOE is to analyse several input variables
called treatment of factors and single output variables called dependent or
yield.
Basic Principle of Design of Experiment
The basic principles of a design of experiment are
1. Randomization
2. Replication
3. Local Control
Randomization
The first principle of an experimental design is
randomisation, 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.
Objectives of Randomization
i. Randomisation helps in the use of probability, which
is helpful in drawing accurate statistical inferences.
ii. Randomisation is used to control bias and extraneous
sources of variation present in the experimental units.
The second principle of an experimental design is
replication, which is the repetition of a basic experiment. It is a complete run
for all treatments to be tested in the experiment. Some variation is introduced
because of the fact that the experimental units are not physically identical,
and this type of variation can be removed by using a number of experimental
units.
Objectives of Replications:
i. To secure a more accurate estimate of the experimental error.
ii. To decrease the experimental error.
iii. To obtain the
most precise estimate of the mean effect of treatment.
Local Control
The third principle of an experimental design is local
control. Some sources of variation can be minimised or removed by randomisation
and replication, but not all. Local control is used to choose a design in such a
manner that all extraneous sources of variation are brought under control. The
term local control refers to the amount of balancing block and grouping of the
experimental units.
- Read: Complete Randomized Design
- Read More: Introduction to Statistics
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