Gul Shair Sumalani M.Phil English Applied Linguistics.

English Language Centre University of Baluchistan Quetta.

Experimental Research Design

What is Experimental Research Design?

The experimental method is the only method of research that can truly test hypotheses concerning cause-and-effect relationships. It represents the most valid approach to the solution of educational problems, both practical and theoretical, and to the advancement of education as a science.

Gay, L. R. (1992). Educational research (4th Ed.). New York: Merrill. (p.298).

What is experimental research Design?

In an experiment, you test an idea (or practice or procedure) to determine whether it influences an outcome or dependent variable. You first decide on an idea with which to “experiment,” assign individuals to experience it (and have some individuals experience something different), and then determine whether those who experienced the idea (or practice or procedure) performed better on some outcome than those who did not experience it.

Brief history of experimental design

According to Ary, Jacobs, and Razavieh (1990), the roots of experimental design began in the 19th century with physical science. This was an attempt to improve observation by deliberately eliminating contextual complexity. It was found successful in scientific observation, and by the end of the 19th century, experimental design was applied to psychology and then to education.

Groups and Tests.

Experimental group: A group assigned to receive some experimental treatment.

Control group: A group assigned to be untreated or to receive a treatment other than the experimental treatment.

Pretest: A test or questionnaire given at the beginning of some treatment.

Post test: A test or questionnaire given at the end of some treatment period.

Variables and their categories.

The dependent variable: The dependent variable is the major variable that will be measured (Hatch & Lazaraton, 1991, p 63). A dependent variable cannot be identified in isolation because it is related to the independent variable. The dependent variable is the variable of focus--the central variable--on which the other variables will act. It is usually the test and what it represents.

The independent variable: it is the variable that the researcher suspects may relate to or influence the dependent variable. In a sense, the dependent variable “depends” on the independent variable (Hatch & Lazaraton, 1991, p. 64). The researcher selects independent variables to determine their effect on or relationship with the dependent variables (Brown, 1988, p. 10).

Variables and their categories

Control variable: A control variable is not of central concern in a particular research project, but might affect the outcome. Control variables are kept constant, neutralized, or otherwise eliminated so that they will not affect the study (Brown, 1988, p. 11).

Intervening variables: Intervening variables are abstract theoretical labels applied to the relationship that links the independent and dependent variables. They are constructs that may explain the relationship between independent and dependent variable, but are not directly observable themselves like, knowledge, memory, thinking etc. (Brown, 1988, p. 12).

Extraneous Variables : Extraneous variables are variables that can interfere with the action of the independent variable. Like Temperature, light, noise, time of the day. Since they are not part of the study, their influence must be controlled.

Methods of controlling extraneous variables include :

Randomization: Randomization comes into play when we randomly assign subjects to experimental and control groups, thus ensuring that the groups are as equivalent as possible prior to the manipulation of the independent variable. Random assignment assures that the researcher is unbiased. Instead, assignment is predetermined for each subject.

Homogeneous Sample: One simple and effective way of controlling an extraneous variable is not to allow it to vary. We may choose a sample that is homogenous for that variable. For example, if a researcher believes that gender of the subject might affect the dependant variable, he/she could select the subjects of the desired

gender only.

Methods of controlling extraneous variables include :

Matching : When randomization is not possible, or when the experimental groups are too small and contain some crucial variables, subjects can be matched for those variables. The experimenter chooses subjects who match each other for the specified variables. One of these matched subjects is assigned to the control group and the other to the experimental group, thus ensuring the equality of the groups at the outset.

Building Extraneous Variables into the Design : When extraneous variables cannot be adequately controlled by randomization, they can be built into the design as independent variables. They would have to be added to the purpose of study and tested for significance along with other variables. In this way, their effect can be measured and separated from the effect of the independent variable.

Types of Experimental Designs

Pre-experimental designs – They are least effective and provide little or no control of extraneous variables.

True experimental designs – Employ randomization to control the effects of variables such as history, maturation, testing, statistical regression, and mortality.

Quasi-experimental designs – Provide less satisfactory degree of control and are used only when randomization is not feasible.

Factorial designs- More than one independent variables can be manipulated simultaneously. Both independent and interaction effects of two or more than two factors can be studied with the help of this factorial design.

Symbols used in experimental design

In discussing experimental designs a few symbols are used. E – Experimental group C – Control group X – Independent variable Y – Dependent variable R – Random assignment of subjects to groups Yb – Dependent variable measures taken before experiment /

treatment (pre-test) Ya – Dependent variable measures taken after experiment/ treatment

(Post-test)

Mr – Matching subjects and then random assignment to groups.

Validity of Experimentation.

An experiment must have two types of validity: internal validity and external validity (Campbell and Stanley, 1963):

Internal validity :

Internal validity refers to the extent to which the manipulated or independent variables actually have a genuine effect on the observed results or dependent variable and the observed results were not affected by the extraneous variables. This validity is affected by the lack of control of extraneous variables.

Validity of Experimentation.

External validity :

External validity is the extent to which the relationships among the variables can be generalized outside the experimental setting like other population, other variables. This validity is concerned with the generalizability or representativeness of the findings of experiment, i.e. to what population, setting and variables can the results of the experiment be generalized.

Factors affecting validity of experimentation :

Campbell and Stanley (1963) have pointed out the following major variables which affect significantly the validity of an experiment:

History :History can be defined as “events, other than the experimental treatment, occurring between pretest and posttest and thus providing alternate explanations of effects” (Campbell & Russo, 1999, p. 80). To put it another way, things that are happening that the researcher is unaware of (Ary, Jacobs, & Razavieh, 1990).

Maturation : The changes that occur in the subjects over a period of time and confused with the effects of the independent variables.

Testing : Pre-testing, at the beginning of an experiment, may be sensitive to subjects, which may produce a change among them and may affect their post-test performance.

Factors affecting validity of experimentation :

Measuring Instruments: Different measuring instruments, scorers, interviewers or the observers used at the pre and post testing stages; and unreliable measuring instruments or techniques are threats to the validity of an experiment.

Statistical regression: It refers to the tendency for extreme scores to regress or move towards the common mean on subsequent measures. The subjects who scored high on a pre-test are likely to score relatively low on the retest whereas the subjects who scored low on the pre-test are likely to score high on the retest.

Factors affecting validity of experimentation

Experimental mortality : It refers to the differential loss of subjects from the comparison groups. Such loss of subjects may affect the findings of the study. For example, if some subjects in the experimental group who received the low scores on the pre-test drop out after taking the test, this group may show higher mean on the post-test than the control group.

Differential selection of subjects : It refers to difference between/among groups on some important variables related to the dependent variable before application of the experimental treatment.

Norms of scientific research

The norms of scientific research are: The researcher must be competent to conduct the research. Consequences of the research must be identified: Procedures

must respect privacy, ensure confidentiality, maximize benefits, and minimize risks..

The sample selection must be appropriate for the purposes of the study, representative of the population to benefit from the study, and sufficient in number.

Norms of scientific research

The participants must agree to participate in the study through voluntary informed consent—that is, without threat or undue inducement (voluntary), knowing what a reasonable person in the same situation would want to know before giving consent (informed), and explicitly agreeing to participate (consent).

The researcher must inform the participants whether harm will be compensated.