Randomized design

Research -CRD

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CONCEPT AND APPLICATION
RANDOMIZED
DESIGN

2. 3
INTRODUCTION
Designing an experiment means deciding how the observations or
measurement should be taken to answer a particular question in a
valid, efficient and economical way. A well designed experiment
helps the workers to properly partition the variation of the data
into respective component in order to draw valid conclusion.

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Experimental Designs
Aim: The main objective of design of experiments is to control the
insignificant variables so that the results could be attributed to
experimental variables.
A Statistical design is a plan for the collection
and analysis of data

4. principle 1
Randomization
principle 2
Replication
principle 3
Local control
1 2 3
3 basic principles of experimental designs are:

5. Randomisation
to eliminate bias
To ensure independance among
observations
Required for valid significance tests and
interval estimates
1
Replication
A repetation of a treatment in an
experiment.
2
Local control
The main objective/ purpose of local control is to
increase the efficiency of experimental design
by decreasing the experimental error
3

6. Technique 1
One way classification -
Completely Randomised
design (CRD)
Technique 2
Two way classification -
Randomised block design
(RBD)
Technique 3
Latin Square design
1 2 3
Techniques of analysis of variance

7. COMPLETELY
RANDOMIZED DESIGN
(CRD)

8. most simplest of all the design
based on randomization and
replication. In CRD, all
treatments are randomly
allocated among all
experimental subjects.
Completely
Randomized
design
All treatments are assigned randomly
among all edxperimental subjects. This
allows experimental unit to have an
equal probablity of recieving any one
treatment
This is suitable only if the experimental
material is homogeneous. eg. laboratory
experiments , green house studies etc.
For the CRD, any difference among
experiment units recieving the same
treatment is considered as experimental
error.

9. Completely
Randomized
design All treatments are randomly allocated
among all experimental subjects. This
allows every experimental unit to have an
equal probability of recieving a treatment
In this design, we would randomly select
60 students and randomly split them into
two groups with 30 each. One group does
not take the practise exam, while the
other does. We have the two groups then
take the actual exam and we compare
results.

10. Advantages
Advantage 1
CRD has several
advantages it is easy to
layout the design
Advantage 3
The number of replication
need not to be same for
each treatment.
Advantage 2
There is complete flexibility in
the number of treatments and
number of replication which
may vary from treatment to
treatment
Advantage 4
The CRD provides
maximum degrees of
freedom for the
experiments of
experimental error.

11. Disadvantages
The main objection against the CRD is
that the principle of local control has
been used in the design. so that the
experimental error is inflated by the
presents of the entire variation among
experimental units.

12. Uses of CRD
1
Under conditions where the
experimental material is
homogeneous eg. Physics,
Chemistry in Chemical and
biological experiment in
some green house studies
3
CRD may be used in chemical
experments where the
exerimental units are the part
of the thoroughly mixed
chemical or powder.
2
In small experiments where
there is a small number of
degrees of freedom

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