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Experimental Research

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Definition

Experimental research attempts to establish

a cause-and-effect relationship between two

phenomena.

It is basically quantitative

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Purpose

The researcher hypothesizes that one

variable, the independent variable, causes

changes in another variable, the dependent

variable.independent variable affects dependent variable

The purpose of the experimental design is to

eliminate alternative hypotheses. If we can

successfully eliminate all alternative

hypotheses, we can argue-by a process of

elimination- that the independent variable is

the cause.

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Example

A researcher may wish to determine

whether the explicit teaching of cultural

background information to university ESLstudents will increase their

comprehension of certain texts.

Dependent Variable: comprehension of certain texts

Independent Variable: explicit teaching of cultural backgroundinformation

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Example

Say I am testing whether a new form of

psychotherapy is successful at improving mental

health. I hypothesize that this psychotherapy is the

cause of improved mental health in the research

participants.

I will use an experimental design to eliminate all (or

as many as possible) alternative hypotheses. If I can

eliminate alternative explanations, I will be able to

make the case that the psychotherapy was the causeof the improvements in the research participants.

Dependent Variable: mental health

Independent Variable: a new form of psychotherapy

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Research Question & Hypotheses

The experimenter starts by making a series

decisions that involve narrowing the

question.

Then, he converts the very general

question that guides study into a more

specific question or statement. This specific

formulation is a hypothesis.

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Procedures involved in conducting an

experimental study

Decide on your hypothesis. Select subjects (participants/sample of the study)

Divide subjects into groups if needed.

Administer pretest (measurement before theexperiment begins)

Implement and monitor treatment-Experimental Treatment: The program you wishto assess its effect

-Control Treatment: The existing program

Administer posttest

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Causality & Control

Experimental research attempts to establishcausality, and to be well aware of its limitations.

1- The study of Planned Change: Unlike naturalistic

research in which phenomena are studied in theirnaturally occurring environments, an experiment, bydefinition involves manipulating the situation.

For example, when the researchers compare the effectsof variations in responses to student writing in EFL

classes, they do not study existing classes with existing,naturally occurring variations in teacher feedback. Rather,they design differing response guidelines, ask theteachers to implement them, and examine their effectson student writing.

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).Causality & Control )Cont

2- Random Assignment: The purpose of therandom assignment is to give each subject an equalchance of participating in any one of the experimentalconditions. This is done to ensure that the groups are assimilar to one another as possible. The larger the sample,of course, the more likely that the groups will be similar.

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Validity of Experimental Design

Internal Validity

An experiment is designed to establish a cause-and- effect relationship; that is, the researchers

goal is to be able to conclude that observeddifferences between groups on the dependentvariables are attributable to the treatment, notto other causes.

External Validity(Generalizability of the study)To what other subjects in what other situationsor settings would the results apply?

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Methods of Experimental Control

Physical Control

Gives all subjects equal exposure to the independent

variable.

Controls non experimental variables that affect the

dependent variable.

Selective Control- Manipulate indirectly byselecting in or out variables that cannot be controlled.

Statistical Control- Variables not conducive tophysical or selective manipulation may be controlled

by statistical techniques (example: covariance).