This document discusses experimental research design. It defines experimental research as a method that can truly test hypotheses about cause-and-effect relationships. It then explains key aspects of experimental design including experimental and control groups, pre-tests and post-tests, independent and dependent variables, and methods for controlling extraneous variables like randomization and matching. Finally, it discusses types of experimental designs and factors that can affect the validity of experimental research.

1. Gul Shair Sumalani
M.Phil English Applied Linguistics.
English Language Centre University of
Baluchistan Quetta.
Experimental
Research Design

2. 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).

3. 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.

4. 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.

5. 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.

6. 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).

7. 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.

8. 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.

9. 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.

10. 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.

11. 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.

12. 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.

13. 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.

14. 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.

15. 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.

16. 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.

17. 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.

18. 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.