Between groups design

Brief description of "Between groups design''

1. BETWEEN GROUPS DESIGN Prepared By: Suhail Ahmad Research Scholar, Dept Of Psychology Aligarh Muslim University

2. Research Design The Research design is the detailed plan of investigation. In fact, it is the blueprint of the detailed procedures of testing the hypotheses and analyzing the obtained data. The research design thus maybe defined as the sequence of those steps taken ahead of time to ensure that the relevant data will be collected in a way that permits objective analysis of the different hypotheses formulated with respect to the research problem. The purpose of any research design is to provide a maximum amount of information relevant to the problem under investigation at minimum cost. Basically research designs serve two purposes: First, It answers the research questions as objectively , validly, economically as it is possible. Second, a research design acts as a control mechanism.

3. Basic Principles of Research Design Professor Fisher has enumerated three principles of experimental designs: (1) the Principle of Replication ; (2) the Principle of Randomization; and the (3) Principle of Local Control. (1) Replication : the term replication is a fusion of two words, namely duplication and repetition. It refers to the deliberate repetition of an experiment, using a nearly identical procedure with a different set of subjects ,In a different setting and at a different time. ( 2) Randomization : It is the second basic principle of research design. It makes the test valid . Randomization ensures the independence of the observation which in turn makes the statistical test valid. Not only this when subjects are randomly assigned to the experimental treatments, this automatically controls the extraneous variables, which otherwise are left uncontrolled. Sometimes it has been found that the complete randomization becomes difficult. This is especially true when one is dealing with organismic variables. n such a case investigator is suggested to take the middle path between complete randomization and complete non-randomization.

4. ( 3) Local Control: By local control we mean balancing, blocking and grouping of the subjects or the experimental units employed in the experimental design. The term grouping refers to the assignment of homogenous subjects or experimental units into a group so that different groups of homogenous subjects or experimental units into a group so that different groups of homogenous subjects maybe available for differential treatment. Blocking refers to the assignment of experimental units to different blocs in such a manner that the assigned experimental units within a block maybe homogenous. Balancing refers to the fact that blocking, grouping and assignment of experimental units have been done in such a fashion that the research design appears to be a balanced.

5. Important experiment designs are as follows: ( a) Informal experimental designs: ( i ) Before-and-after without control design. (ii) After-only with control design. (iii) Before-and-after with control design. ( b) Formal experimental designs: ( i ) Completely randomized design (C.R. Design). (ii) Randomized block design (R.B. Design). (iii) Latin square design (L.S. Design). (iv) Factorial designs.

6. Schematic Representation of experimental designs

7. Between Groups Design We will discuss only two types of Between Groups design: Randomized Groups Design Matched Groups design or Randomized Block design. Randomized Groups Design: A Randomized groups design is one in which subjects are randomly assigned to the different groups meant for the different conditions or values of the independent variable. The randomized groups design is based upon the assumption that the random assignment of subjects into two or more groups will make these groups statistically equivalent on the subject relevant variables(attitude, ability, motivation emotions etc) which may produce variations in the dependent variable.

8. When the subjects are randomly assigned to only two groups, the resulting design is known as two-randomized groups design and when the subjects are randomly assigned into more than two groups, the resulting design is called multi-group design or more than two randomized groups design. So in two-randomized groups design the experimenter selects two values of an independent variable. These two values may also be called “conditions” or “treatments” of the experiment. His main interest is to examine whether or not these two conditions affect the dependent variable in a differential way. Usually t-test or a non-parametric substitute namely Mann whitney –U test is used as a statistical analysis in two-randomized groups design. Underwood(1966) has suggested two primary ways through which unbiased groups or random groups of subjects can be formed in order to achieve the successful random assignment. These are: (A) Captive Assignment (B) Sequential Assignment

9. Matched Groups Design or randomized-block design: This may be a two-matched or More-than two-matched groups design. In a matched- groups design all subjects are first tested on a common task or a pretest measure(also called a matching variable) and then, they are formed into groups(as many as needed for the experiment) on the basis of performance on the common task or the matching variable. The groups thus formed are said to be equivalent groups. Subsequently, the different conditions or values of the independent variable are introduced to each group. If these groups have equivalent means on the dependent variable before the experimental treatment is given and if a significant difference occurs after administering the experimental treatment and controlling the relevant variables, the resulting differences in the dependent variable wil be attributed to the experimental treatment.

10. Methods of Matching: Having selected a matching variable a set of scores earned by all subjects on the matching variable , the next step is to match them . There are two ways of matching : (1) Matching By Pairs : On the basis of the obtained scores by the subjects , the experimenter matches subjects in a way that each subject has a corresponding partner in a matched group or groups . (2) Matching on the basis of Mean and Standard deviation: The experimenter forms as many groups as needed for the experiment in a way that their subsequent means and standard deviations do not differ significantly.

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