Chapter 7






The major differences between causal-comparative and experimenta l research is that in the experiment the researcher controls the alleged independent variable. In fact, the experiment is the quantitative approach that provides the greatest degree of control over the research procedures. The experimental researcher controls the selection of participants for the study and divides the selected participants into two or more groups having similar characteristics at the start of the experiment . The researcher then applies different programs or treatments to the groups. The researcher also controls conditions in the research setting, such as when the treatments are applied, by whom, and for how long. Finally, the researcher selects a test or measure to determine the effects of the treatments on the groups.

      It is the selection of participants from a single pool and the ability to apply different treatments or programs to participants with similar characteristics that separates  experimenta l from causal-comparative research. The essence of experimentation is control, although in many education settings it is not possible or feasible to meet the stringent control conditions required by experimental research.

      The following are examples of experimental studies:

  1. The comparative effectiveness of personalized instruction from a teacher versus computer instruction on computational skills . The independent variable is type of instruction (personalized teacher instruction versus computer instruction); the dependent variable is computational skills. A group of students who had never experienced either personalized teacher instruction or computer instruction would be selected and randomly divided into two groups, each taught by one of the methods. After a predetermined period of time, the students’ computational skills would be measured and compared to determine which, it either, treatment produced the higher computational skills.
  2. the effect of self-paced instruction on self-concept . The independent variable is pacing(self-pacing versus teacher pacing); the dependent is self-concept. Two groups would be randomly formed from a single group of students who had not previously been exposed to either of the two pacing methods. Each group would receive its respective treatment. After a predetermined time period, their scores on a self-concept test would be compared.
  3. the effect of positive reinforcement on attitude toward school . The independent variable is type of reinforcement (e.g., positive, negative, and no reinforcement); the dependent variable is attitude toward school. In this example three groups will be studied. The three groups would be randomly formed from a large  group of students. One group would receive positive reinforcement, another negative reinforcement, and the third no reinforcement. After the treatments were applied for some period of time, student attitudes toward school would be measured and compared for each of the three groups.


 Experimental Research - An attempt by the researcher to maintain control over all factors that may affect the result of an experiment. In doing this, the researcher attempts to determine or predict what may occur.


Experimental Design - A blueprint of the procedure that enables the researcher to test his hypothesis by reaching valid conclusions about relationships between independent and dependent variables. It refers to the conceptual framework within which the experiment is conducted.


Steps involved in conducting an Experimental Study

1.   Identify and define the problem.

2.   Formulate hypotheses and deduce their consequences.

3.   Construct an experimental design that represents all the elements, conditions, and relations of the consequences.

a.          Select sample of subjects.

b.         Group or pair subjects.

c.          Identify and control non experimental factors.

d.         Select or construct, and validate instruments to measure outcomes.

e.          Conduct pilot study.

f.           Determine place, time, and duration  of the experiment.


4.   Conduct the experiment.

5.   Compile raw data and reduce to usable form.

6.   Apply an appropriate test of significance.


Essentials of Experiment Research

1.   Manipulation of an independent variable.

2.   An attempt is made to hold all other variables except the dependent variable constant - control .

3.   Effect is observed of the manipulation of the independent variable on the dependent variable - observation .


Methods of Experimental Control

1.      Physical Control.

2.      Gives all subjects equal exposure to the independent variable.

3.      Controls non experimental variables that affect the dependent variable.

4.      Selective Control - Manipulate indirectly by selecting in or out variables that cannot be controlled.

5.   Statistical Control - Variables not conducive to physical or selective manipulation may be controlled by statistical techniques (example: covariance).


Validity of Experimental Design

1.      Internal Validity asks did the experimental treatment make the difference in this specific instance rather than other extraneous variables?

2.      External Validity asks to what populations, settings, treatment variables, and measurement variables can this observed effect be generalized?


Tools of Experimental Design used to control factors Jeopardizing  Validity

1.      Pre-Test - The pre-test, or measurement before the experiment begins, can aid control for differential selection by determining the presence or knowledge of the experimental variable before the experiment begins. It can aid control of experimental mortality because the subjects can be removed from the entire comparison by removing their pre-tests. However, pre-tests cause problems by their effect on the second measurement and by causing generalizability problems to a population not pre-tested and those with no experimental arrangements.

2.      Control Group -The use of a matched or similar group which is not exposed to the experimental variable can help reduce the effect of History, Maturation, Instrumentation, and Interaction of Factors. The control group is exposed to all conditions of the experiment except the experimental variable.

3.      Randomization - Use of random selection procedures for subjects can aid in control of Statistical Regression, Differential Selection, and the Interaction of Factors. It greatly increases generalizability by helping make the groups representative of the populations.

4.      Additional Groups - The effects of Pre-tests and Experimental Procedures can be partially controlled through the use of groups which were not pre-tested or exposed to experimental arrangements. They would have to be used in conjunction with other pre-tested groups or other factors jeopardizing validity would be present.



Wed, 11 May 2011 @15:23

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