PYSC 224 Introduction to Experimental Psychology · PDF filePYSC 224 Introduction to Experimental Psychology ... sources of extraneous variables ... are maturing at different rates

College of Education

School of Continuing and Distance Education 2015/2016 – 2016/2017

PYSC 224

Introduction to Experimental

Psychology

Session 7 – Extraneous Variables

Lecturer: Dr. Margaret Amankwah-Poku, Dept. of Psychology Contact Information: [email protected]

mailto:[email protected]



Session Overview

• Extraneous variables are any variable other than the independent variable that can influence the dependent variable

• In experimentation, an experimenter has to control extraneous variables in order to establish cause effect relationship and achieve internal validity

• There are general extraneous variables, as well as participant and experimenter effects which can all act as threats to internal validity during experimentation, if they are not controlled

Dr. Margaret Amankwah-Poku Slide 2

Session Goals and Objectives

At the end of this session, you should be able to

• Define what an extraneous variable is and distinguish it from an independent variable

• Discuss the various types of general extraneous variables

• Outline participant and experimenter effects as sources of extraneous variables

• Explain how extraneous variables act as threats to internal validity in experimentation


Session Outline

The key topics to be covered in the session are as follows:

• What are extraneous variables?

• General extraneous variables

• Participant effects

• Experimenter effects


Reading List

• Christensen, B.L. (1997). Experimental Methodology (7th ed.). Boston: Allyn & Bacon. (p. 229-256)


WHAT ARE EXTRANEOUS VARIABLES?

Topic One


What are Extraneous variables?

• Any variable other than the independent variable that can influence the dependent variable

• The greater the potential impact of extraneous variables the lesser the validity and reliability of the results

• Extraneous variables reduce internal validity

• Thus, an experimenter has to identify potentially extraneous variables and control them



• According to Heiman (1995) an experimenter can use the four general components of any study to help identify extraneous variables in an experiment

• “The experimenter observes participants in a specific environment and applies a measurement procedure” (Heiman, 1995)

Slide 8


• That is:

Experimenter variables

Participants variables

Environmental variables

Measurement variables


Extraneous Variables

• Types of extraneous variables

1. General extraneous variables

2. Participants effect

3. Experimenter effect


GENERAL EXTRANEOUS VARIABLES Topic Two


General extraneous variables

• Campbell & Stanley (1963) identified six general sources of extraneous variables that act as threats to internal validity


General extraneous variables

• 1. History

• 2. Maturation

• 3. Instrumentation

• 4. Statistical regression

• 5. Selection Bias

• 6. Mortality / Attrition


1. History

• Events that take place between pre and post

measurements of the dependent variable, that can affect the outcome of the experiment

• They become probable rival hypotheses concerning the change that occurred between the pre and post measurements


1. History

• E.g- The effect of time lapse on students’ perception about Experimental Psychology

• If there is a change in perception, one will not be able to conclude precisely that this is as a result of the time lapse

• A change in perception may be due to an event (e.g. a test) that occurred and not because of the time lapse (independent variable)


1. History

• Example: Effect of anger management on violent secondary school children

• If aggressive behaviour decreases, can we conclude that treatment has been effective?

• History effect- something else in the school environment may have caused a decrease—e.g. less overcrowding, an aggressive student arrested by the police etc.


2. Maturation

• Maturation refers to changes in the internal conditions of the individual due to the passage of time

• Changes are both biological and psychological processes, e.g. age, learning, fatigue, boredom and hunger

• These are not related to specific external events but reside within the individual

• Maturation is a more critical problem in research involving children


2. Maturation

• Example: Effect of anger management on violent secondary school children


• Maturation effect: between observations, participants could have grown out of their aggressive behaviour


3. Instrumentation

• Changes that occur over time in the

measurement of the dependent variable

• Being in an experiment or being tested can influence people’s performance in a later test or administration of test


3. Instrumentation

• First, participants may learn how to take the tests thus, later behaviour is changed by the earlier experience

• Example- You write a class test the first time and you do not perform well but you perform better on a second test

• This is called testing effect


3. Instrumentation

• Second, some techniques used to measure the

dependent variables may be subject to change during the course of a study

• Example- there may be unobserved changes in criteria used by observers or in instrumentation calibrations

• This is called instrument decay


3. Instrumentation

• Example: Effect of anger management on violent secondary school students


• Testing effect: the act of assessing aggression may have led to awareness of students’ own aggression


4. Statistical Regression

• This is the lowering of extremely high scores or

the raising of extremely low scores during post-testing

• This may occur because participant were selected for a study due to their extremely high or extremely low score on some characteristics


4. Statistical Regression

• Thus, when they are retested, the scores tend

to change in the direction of the mean

• Extremely high scores are likely to become lower, and extremely low scores are likely to become higher

• Example- Extremely heavy smokers selected for relaxation training to reduce smoking


5. Selection Bias

• Choosing participants for the various treatment groups on the basis of different criteria

• Participants are selected from an existing natural group resulting

• A typical example is when a researcher uses the non-equivalent control group design


5. Selection Bias

• Selection can interact with maturation, history or instrumentation, mortality and regression

• Example- selection by maturation interaction can occur when experimental groups selected are maturing at different rates


6. Mortality/ Attrition

• The differential loss of participants from the various comparison groups in an experiment

• This may produce differences in the groups that cannot be attributed to experimental treatment

• Participants who drop out from the experiment may be different from those who complete it


6. Mortality/ Attrition

• Example- Running a stress management program for hypertensive patients for 8 weeks

• After 4 week some participants decide to drop because they have manageable blood pressure levels

• Thus, only those with very high levels will complete 8 weeks


PARTICIPANT EFFECTS Topic Three


Participant effect

• Examples of participant effect as extraneous variables are

Demand characteristic

Good participants tendency

Evaluation apprehension

Negative attitude


Participant effect

1. Demand characteristics

• Cues provided by the research context that guides or biases participants’ behaviour in a research

• Any variables in an experiment such as

• The instructions, experimenter, rumours or the experimental setting from which participants create their perception of the purpose of the experiment


Participant effect

2. Good participants tendency

• The tendency of participants alter their behaviour to act according to what they think the experimenter wants

• Example- participants may deliberately feign a naive attitude about a particular issue (a teenager and drug use)


Participant effect

3. Evaluation apprehension

• The tendency of participants to alter their behaviour in order to appear as socially desirable as possible

• Sometimes occur when participants think that the experiment is measuring their competence (feedback and performance)


Participant effect

4. Negative attitude

• Some participants go to a laboratory with a negative attitude to ruin an experiment

• Usually occurs when participants are required or forced to be in an experiment


EXPERIMENTER EFFECTS Topic Four


Experimenter Effect

• Any change in participants’ performance that can be attributed to the experimenter

• It includes

Experimenter attribute

Experimenter expectancies


Experimenter Effect

1. Experimenter Attributes

• Physical and psychological characteristics of an experimenter that may create differential responses in participants

• Rosenthal (1966) proposed 3 categories of attributes

• a. Biosocial attributes: such as experimenter’s age, sex, race and religion


Experimenter Effect

• b. Psychosocial attributes: Experimenter’s anxiety level, need for social approval, hostility, authoritarianism, dominance, social behaviour, intelligence, etc.

– c. Situational factors: Whether or not (1) the experimenter and participants have had previous contact, (2) the experimenter is a naïve or experienced one (3) the subject is friendly or hostile


Experimenter Effect

2. Experimenter Expectancies/ Bias

• The influence of the experimenter’s expectations regarding the outcome of an experiment

• The experimenter’s expectations can lead him/her to behave unintentionally in ways that will bias the results of the experiment in the desired direction


END OF SESSION 7

References

• Campbell, D. T. & Stanley, J. C. (1963). Experimental and Quasi-Experimental Designs for Research. London. Houghton Mifflin Company

• Christensen, B.L. (2007). Experimental Methodology (10th ed.). Boston: Allyn & Bacon. (p. 83-90, 305-309, 321-322)

• Heiman, G. A. (1995). Research methods in psychology. Boston: Houghton Mifflin.

• Rosenthal, R. (1966). Experimarer effects in behavioral research. New York: Appleton-Century- Crofts.


PYSC 224 Introduction to Experimental Psychology · PDF filePYSC 224 Introduction to Experimental Psychology ... sources of extraneous variables ... are maturing at different rates

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