True and Quasi-Experiments

The experimental method is the only method that attempts to show "effectiveness" (keberkesanan) of a particular treatment (eg. teaching method, curriculum innovation, counselling technique and so forth). It is a method that can claim to show "cause" and "effect". In other words, to show whether the inquiry method "causes" students to perform better on critical thinking ("effect"), the experimental method will have to be used. Hence, it is important that you use the word "effectiveness" carefully, as it only applies if  you are using the experimental method.

What is an Experiment?
An experiment is a researh method in which the researcher wants to know  the effect of using a particular treatment on a group of subjects. To show that a particular treatment has an effect, the researcher has to control all other factors that might influence the subjects. See Figure above. The reseacher is interested in establishing:

"The effectiveness of the inquiry method in enhancing critical thinking in science among primary school students"

Upom completion of this module you should be able to:
  • define what is an experiment
  • differentiate between true and quasi experiments
  • explain the need to ensure internal validity of experiments
  • discus the importance of external validity of experiments

  • Remember more and think faster with BE SMART”
  • “Rewarding pre-schoolers with chocolates has improved  attention in class”
  • “The Mental Awareness Approach has proven to be an  effective way to help smokers give up the habit”
  • “Cognitive therapy is an effective method for treating drug   addicts”
  • “Enhancing self-esteem improves academic performance”
Have you come across these statements or somewhat similar statements? Note that each statement is making a claim that their proposed method, technique or procedure is effective in enhancing human performance. Before accepting the clain, you would like to know how they went about proving effectiveness. How does one prove effectiveness? We can prove effectiveness using the experimental method. You may have conducted science experiments in the laboratory or in the field!
The experimental method is the most scientific of methods used in the behavioural sciences. Its origins are traced to the field of agriculture where experiments were conducted to test the effectiveness of various kinds of treatments (eg. fertilisers) on plant growth and yield. The method is also widely used in the medical sciences especially in testing the effectiveness of various kinds of treatments (eg. new drugs, methods, procedures) on patients. The experimental method is widely used in education in which researchers observe the occurrence of a phenomenon as a consequence of a particular action.
Science Critical Thinking Test
Experiments can be divided into "TRUE" Experiments and "QUASI Experiements". The "true" experiment is one in which subjects are randomly assigned to the experimental and control groups.

Science Critical Thinking Test
The key problem in conducting experiments is establishing suitable CONTROL,so that any change in the posttest can be attributed only to the treatment that was manipulated by the researcher. Control means ruling out other possible causes for the changes on the posttest.
There are many extraneous variables that need to be controlled so that they do not contaminate or interfere with the findings on the posttest. Once an extraneous variable creeps into an experiment, the researcher can no longer draw any conclusion regarding the causal relationship that exists between the independent and the dependent variable (Christensen, 1988).
For example, the attitude of students, their interests in science, their social skills, their self-efficacay and so forth. The problem of control is more serious in educational experiments where it is difficult HOLDING all variables constant that might affect the posttest.
Science Critical Thinking Test
NO Treatment

Science Critical Thinking Test

                "It is an experimental design that does not meet all the
           requirements necessary for controlling the influence
           of extraneous variables"

If you want to make establish whether variable X caused variable Y, the researcher should conduct a "true experiemnt". A true experiment means that the sample should be randomly selected. If you cannot use random assignment to design a true experiment, a "quasi experiment" is the second best choice accoridng ot Campbell and Stanley (1967). A quasi experiment is not as good as true experimentm but it is far superior than some weak experiments. When you are unable to ensure random assignment, you have to settle for a "Quasi-Experiment".  Howver, the reseacher should be aware of the special problems that may arise when subjects are not assigned randomly to groups, and should take steps to solve them" (W. Borg & M. Borg, (1988). Educational Research: An Introduction, p.680).
In educational research, many studies are based on a quasi-experimental because of the difficulty of conducting random assignment of subjects in educational institutions. Many studies in education are conducted in real world settings; i.e. in the classroom and seldom in laboratoies where the researcher has more autonomy to manipulate and assign subjects. In school settings, administrators are reluctant in moving students around and assigning them to an experimental or control group. They argue that It will lead to disruption of the daily running of teaching and learning and hence are unwilling to allow researchers to assign students as they wish. Hence, researchers have to settle for "intact classes" in which all subjects in a class are taken to be either the experimental or control group.

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Table of Random Numbers
Table of Random Numbers
A popular technique used to ensure random assignement is to use the Table of Random Numbers. Say you have 100 subjects to be assigned to an Experimental Group and a Control Group. Assign number 1 to 70 to the subjects. Then, refer to the Table of Random Number and select a starting point, let's say the top of the fourth column has the numbers 31, 45, 38, 63, 63, 34 and so forth. You will select subject no. 31 assigned to the Experimental Group followed by subject no. 45 assigned to the Control Group. Of course you will ignore number 76 because it is outside the 70 subjects. You will continue this procedure until all 70 subjects have been assigned to the two groups.
"Quasi experiments are research designs that do not have randomly assigned treatment and comparison groups. Instead the comparisons between treatment and nontreatment conditions must always be made with nonequivalent groups or with the same subjects prior to treatment. If you cannot randomly assign people or groups to treatment conditions, you lose the ability to control what happens to whom.
You can still observe what happens when, and to whom, however; and by deciding what and when to measure, you can design one of several quasi experiments. You forfeit control when you not use random assignment, but you can still conduct research and analyze cause-effect relationships without a true experiment" (L.H.Kidder, Research Methods in Social Relations, 1980, p. 43).
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In education, many experiments are conducted in the classroom (natural setting) and so many factors not related to the treatment may influence performance in the posttest. With reference to Figure 3.1, some students may have discussed with their friends at home concerning the science topic, while others may have viewed a programme on the topic on TV. So, improved performance on the posttest may not be attributed to the treatment but due to the influence of other factors. Therefore, it is necessary to control for the influence of these outside factors or variables in order to attain internal validity.
Some experiments have both an experimental group and a control group. An experimental group consists of subjects who are exposed to the treatment. For example, a particular counselling technique is used for a group of juvenile delinquents. The control group consists of subjects who do not receive the treatment (i.e. they are not ‘treated’ with the counselling technique). Comparison between the experimental group and the control group determines the effectiveness of the counselling technique. In some experiments there may be more than one experimental group; subjects treated with two or three different methods or techniques or procedures are compared with the control group who do not receive any of the treatments. You can also compare the effectiveness of different treatments on the dependent variable
  • What is unique about the experimental method compared to other methods of research?
  • What is ‘treatment’?
  • What is the difference between an experimental group and a control group? Why do you need these two groups?