EXPERIMENTAL DESIGNS

                              EXPERIMENTAL   DESIGNS

               “WHENEVER THERE IS A CAUSE AND THERE WILL BE AN EFFECT”

INTRODUCTION:

“An experiment is an observation under controlled condition”

                                                                                    F.S.Chapin

            Experimental design is the blue print of the procedures that enable the researcher to test the hypothesis by relating independent variables or it enables the researcher to make a meaning interpretation of the results of the results of the study with the help of the statistical analysis of the data.

Pure experimental studies are very rare in social science. Often we conduct crude and quasi-experiments in education.

IMPORTANT TERMS AND SYMBOLS IN EXPERIMENTAL DESIGNS:

EXPERIMENTER:

            It is the person who conducts the experiments. Generally it is denoted by E

SUBJECT:

            It is living organisms that it is studied. It is denoted by S

VARIABLE:

            A concept which can like on different quantitative values is called a variable.

Example:Concepts like height, weight and income etc.,

 a)Independent variable:

            The variable that is antecedent to the dependent variable is termed as independent  variable

b)Dependent variable:

             it is one variable depends upon or is a conservancy of the other variable is termed as a dependent variable.

CONTROL GROUP:

            The group that does not receive any experimental treatment is called control group.

EXPERIMENTAL GROUP:

            The group that is given the independent variable treatment or is exposed to some independent variable is called experimental group.

PRE TEST:

            It is the test that is administered to the subjects before the independent variable. It is represented by the symbol T₁ .

POST TEST:

            It is the test that is administered to the subjects after the independent variable. It is represented by the symbol T_2.

       Validity of Research Design:

               A very significant contribution to the evaluation of research designs has been made by Campbell and Stanley, who suggest that there are two general criteria of research design.

• Internal validity
• External validity

     Internal validity:

      Internal validity is essentially a problem of control. The design of appropriate controls is matter of finding ways to eliminate extraneous variables (i.e.) variables that could lead to alternative interpretations. Anything that contributes to the control of a design contributes to its internal validity.

     External validity:

              External validity refers to the generalizability or representativeness of the findings. When experimental controls are tightened to achieve internal validity, the more artificial, less realistic situation may prevail, reducing the external validity or generalizability of the experiment. Some compromise is inevitable so that a reasonable balance may be established between control and generalizability between internal and external validity.

  Experimental Design:

     Experimental design is the blueprint of the procedures that enable the researcher to test the hypotheses by reaching valid conclusions about relationships between independent and dependent variables. Selection of a particular design is based on the purposes of the experiment, the type of variables to be manipulated, and the conditions or limiting factors under which it is conducted.

          The adequacy of experimental designs is judged by the degree to which they eliminate or minimize threats to experimental validity. Three categories are presented here:

1.      Pre-experimental design is the least effective, for it provides either no control group or no way of equating the groups that are used.

2.      True-experimental design employs randomization to provide for control of the equivalence of groups and exposure to treatment.

3.      Quasi-experimental design provides a less satisfactory degree of control, used only when randomization is not feasible.

        R - random assignment of subjects to groups or treatment

       X - exposure of a group to an experimental variable

       C - exposure of a group to the control condition

       O - Observation

1. Pre-Experimental Design:

      The pre-experimental design does not provide a control or the equivalent of a

Control group.

A.    The Single-Group, Posttest Design:

              Here a group is exposed to some form of intervention and then subsequently tested. This design might be illustrated as shown below

               Experimental Group      -         Processed Observed or Measured

                                     (X)                                                   (O)

            

                Carefully studied results of a treatment are compared with a general expectation of would have happened if the treatment had not been applied. This design provides the weakest basis for generation.

                                 In a test administered after the showing of the film, the mean score was 86. The mean score was higher that it would have been had the film not been viewed and, as he recalls, higher than the mean score of a test that he had administered to a similar class several years before. He concludes that the film has been effective in reducing racial prejudice.

               The reader has no way knowing if a change has occurred because lack of pretest or if a similar group who had not seen the film (a control group) would have scored differently from the group viewing the film. This design is the poorest available and should not be used.

B. The   Single-Group, Pretest-Posttest Design:

                          This design is an improvement over the above design because the effects of treatment (X) are judged by making a comparison between pre-test and post-test scores. However, no control group is used in this design.

Experimental group – pre-test O₁ - Special Treatment X – Post-test O₂

            In the same setting we have to administer a pre-test before showing the film and a posttest after the viewing. He computed the mean difference between the pretest and the posttest scores and found that the mean had increased from 52 to 80, a mean gain of 28 score points. It also apparently detected some temporary improvement in attitude toward racial integration. He concludes that there has been a significant improvement in attitude as a result of students viewing the film.

C. The Static – Group Comparison Design:

               This design compares the status of a group that has received an experimental treatment with one that has not. There is no provision for establishing the equivalence of the experimental and control groups, a very serious limitation.

           Experimental Group             -                    (X......O₁) Group Tested (O₁)

                                       

           Control Group                       -                    Group Tested (O₂)

                                A beginning researcher administered the 25-minute racial integration film to a group of elementary teachers in one school. He then administered the attitude scale and computed the mean score. At another elementary school he administered the attitude scale to teachers who had not viewed the film. A comparison of mean scores showed that the teachers who had viewed the film had a higher mean score than those who had not. He concluded that the film was an effective device in reducing racial prejudice. The dotted line indicates that the control group (O1) has not been equated by randomization.

      2. True Experimental Design:

          In a true experiment the equivalence of the experimental and control groups is provided by random assignment of subjects to experimental and control treatments. Although it is difficult to arrange a true experimental design, particularly in school classroom research, it is the strongest type of design and should be used whenever possible. There are three types of experimental designs are discussed here,

   A. Randomized Two Groups – Treatment and Posttest Design:

           This design is the most effective and useful true experimental design, which minimizes the threats to experimental validity.

    Randomly picked                       Special Treatment (X)        Post-test (O₁)

      experimental group (R)           

   Randomly picked

     Control group (R)                     No Special Treatment         Post-test (O₂)

            This design is one of the most effective in minimizing the threats to experimental validity. It differs from the static group comparison design in that experimental and control groups are equated by random assignment. At the conclusion of the experimental period the difference between the mean test scores of the experimental and control groups is subjected to a test of statistical significance, usually a t test  or an analysis of variance. The assumption is that the means of randomly assigned experimental and control groups from the same population will differ only to the extent that random sample means from the same population will differ as a result of sampling error. If the difference the means is too great to attribute to sampling error, the difference may be attributed to the treatment variable effect. 

B. Randomized Two Groups Pretest, treatment and Posttest Designs:

             These types of design have been described as true experimental designs because they always include the processes of randomization.

          Randomly picked   -     Pre-test (O₁) -   Special Treatment (X) - Post-test (O₂)

      experimental group (R)                                                                                                                                                                                                                                                                                                                                                         

  Randomly picked    -     Pre-test (O₃) - No Special treatment   - Post-test (O₄)

Control group (R)

 This design is similar to the previously described design, except that pretests are administered before the application of the experimental and control treatments and posttest at the end of the treatment period. Pretest scores can be used in analysis of covariance to statically control for any differences between the groups at the beginning of the study. This is a strong design, but there may a possibility of the influence of the interaction effect of testing with the experimental variable.

 The Solomon Four-Group Design:

               The Solomon Four Group Design developed by Solomon (1949)is really a combination of the two equivalents – groups design, namely, the post-test – only design and pre-test – post-test only design and represents the first direct attempt to control the threats of the external validity.

Randomized group -   Pre-test - Receives intervention    -         Post-test

         R         (A)                     O₁                              X                           O₂ 

Randomized group   - Pre-test   - No intervention        -       Post-test

         R          (B)                    O₃                                                    O₄

Randomized group           -             Receives intervention   -          Post-test

         R         (C)                                                                                        O₅

Randomized group            -            No intervention      -                 Post-test

         R        (D)                                                                                         O₆

              The design is really a combination of the two-group designs previously described, the posttest only and the pretest-posttest. The Solomon Four-Group Design permits the evaluation of the effects of testing, history and maturation. Analysis of variance is used to compare the four posttest scores; analysis of covariance may be used to compare changes in O₂ and O₄.

                This design provides for two simultaneous experiments, the advantages of a replication are incorporated. A major difficulty is finding enough subjects to assign randomly to four equivalent groups.

3. Quasi – Experimental Designs 

                 These designs provide control of when and to whom the measurement is applied, but because random assignment to experimental and control a treatment has not been applied, the equivalence of the groups is not assured.

A. The Non-equivalent Pre-test – Treatment – Posttest Design:

                This design is often used in classroom experiments when experimental and control groups are such naturally assembled groups as intact class, which may be similar.

       Experimental Group - Pre-test (O₁) - Treatment (X) - Post-test (O₂)

       Control Group           - Pre-test (O₃)              -                 Post-test (O₄)

             As in the pretest-posttest equivalent group design, analysis of covariance may be used with the pretest as the covariate. Because this design may be only feasible one, the comparison is justifiable, but as in all quasi-experimental studies, the result should be interpreted cautiously. Difference between the Pretest and posttest (O₁ and O₂) of experimental group and the difference between the Pretest and Posttest of Control group (O₃ and O₄) will give the result of the design.

B. Single Group Time-Series Design:      

            This is the design which consist number of Pretest and Posttest only for Experimental Group. One of the main problems with conducting experiments is that the effects of intervention may be only partially revealed, at the moment of testing.

Experimental Group- Pretest –Pretest-Pretest – Treatment – Posttest-Posttest -Posttest                                                                                 

                                         O₁            O₂        O₃             X                O₄            0₅            O₆

 The diagram showing one X and several Os does not necessarily represent the relative number of sessions for each. It may be that each O represents one measurement, and the single X represents an intervention of several weeks. Although it is better to have several observations, as shown, it is not always possible to have this many. For instance, a time-series experiment by a student of the second author used only two pre-intervention and two post-intervention measures. Because this study was measuring the effect of a program to reduce the number of criminal visualizations of students with disabilities, it was necessary to have a 2-month period between measurements in order to have a sufficient number of victimization for each period measured. Thus, the intervention appeared successful in reducing crimes committed against persons with disabilities.

C.          Control Group Time-Series Design:

                      This design is somewhat related to the previous design. The previous design consist only Experimental Group. Here in this design, we are including Control Group without treatment.

Experimental Group- Pretest –Pretest-Pretest – Treatment – Posttest – Posttest - posttest                                                                                                                       

                                         O₁            O₂        O₃             X                O₄            0₅              O₆

Control Group- Pretest –Pretest - Pretest ––-- Posttest – Posttest -  Posttest                                                                                                                 

                                 O₁            O₂        O₃                O₄            0₅              O₆

                 This design proves the effect of treatment by comparing difference of both the group results. It also gives the importance of number of pretest and posttest among both the groups.

D.    Counter Balanced Design:

             These are designs in which experimental control derives from having all the subjects receive all the treatment conditions. The subjects are placed into, in the case of this example, four groups. Each of the groups then receives all four treatments but in different orders.

                A         Pretest       T₁         T ₂         T₃          T₄      Posttest₅

                        B         Pretest       T ₂        T₃          T₄          T₁      Posttest₅

                        C         Pretest       T₃          T₄          T₁          T₂     Posttest₅

                        D         Pretest       T₄          T₁          T₂          T₃     Posttest₅

      

        A counter balancing design in which four treatments have been randomly given four groups at four different occasions. Variables like history, maturation, testing, instrumental morality posing threats to internal validity are well controlled by the counterbalanced design.

Conclusion

                 Experimentation is a sophisticated technique for problem solving and may not be an appropriate activity for the beginning researcher. It has been suggested that teachers may make their most effective contribution to educational research by identifying important problems that they encounter in their classrooms and by working cooperatively with research specialists in the conduct and interpretation of classroom experiments.

REFERENCE:

·         Methodology of educational research – Lokesh koul

·         Research methodology in education   -Dr.Nagarajan