RANDOMIZE GROUP DESIGN

AMIT KUMAR SHUKLA

M.A. 1ST SEM

D.A.V. PG COLLEGE, VARANASI

DEFINITION:A randomized group design is one in which subjects are randomly assigned to the different groups meant for the different conditions or values of the independent variables

ASSUMPTIONS: The random assignment of subjects into two or more groups will make these groups statistically equivalent on the subject relevant variable which may produce variations in the dependent variable

TYPES1.TWO RANDOMIZED GROUPS DESIGN 2.MULTI GROUPS DESIGN

TWO RANDOMIZED GROUPS DESIGN In this design subjects are randomly assigned to two groups only. Experimenter, first define independent

variable and then dependent variable. Experimenter selects two values of the independent variables. These two values may also be called as

“CONDITIONS” or “TREATMENT” of the experiment.

POPULATION

SAMPLES

GROUP “A” GROUP “B”

EXPERIMENTAL GROUP CONTROL GROUPTREATMENT PROVIDE NO TREATMENT PROVIDE

RANDOM ASSIGNMENT RANDOM ASSIGNMENT

It is expected that these two randomly assigned groups will not differ significantly at the start of experiment.

It is not necessary that in a randomized group design the numbers of subjects in each group should be equal. But the equal N is preferred because it facilitates some statistical calculations (Edward, 1968; Winer, 1971)

UNDERWOOD(1966) has suggested two primary ways through which random groups of subject can be formed:

CAPTIVE ASSIGNMENT: In this technique, all subjects are individually know to the experimenter by name and they all present at one time. In a way there are made captive for the entire duration of the experiment so that they can at random be assigned to the different conditions or groups .

SEQUENTIAL ASSIGNMENT: In this technique , experimenter does not know the details of the subjects. He is simply aware of the fact that a certain numbers of subjects will participate in the experiment.

As the experiment in the randomized group design usually continues for several days or week. The experimenter may use 5 subjects on 1st day, 2 subjects on 2nd day, 6 subjects on 3rd day and so on. Thus the experiment is conducted in a prearranged sequence.

LIMITATIONS: If the subjects are not representative of the original randomly assigned groups, it is obvious that these equivalent groups resulting from random assignment may no longer be really equivalent and then conclusions drawn may not be generalized.

In this design only two values take part in experimentation, it is difficult to state precisely the exact relationship between influential independent variable and dependent variable.

MORE THAN TWO RANDOMIZED GROUPS DESIGN In such a design there are three or more conditions or values of the independent variable

and accordingly, three or more groups of subject participate in the experiment. The design is so called because the total subjects are randomly assigned to three or more unbiased groups.

The process of captive assignment as well as the process of sequential assignment may be utilized as the techniques of random assignment of subjects into three or more groups.

In psychological researches the use of more-than-two randomized group design is more common than the two – randomized group design.

In multi – groups design the two most common statistics applied are the “analysis of variance” and the “Duncan Range Test”.

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