PYSC 224 Introduction to Experimental Psychology Session 7 Extraneous Variables Lecturer: Dr. Margaret Amankwah-Poku, Dept. of Psychology Contact Information: mamankwah-poku@ug.edu.gh College of Education School of Continuing and Distance Education 2015/2016 2016/2017
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 Dr. Margaret Amankwah-Poku Slide 3
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 Dr. Margaret Amankwah-Poku Slide 4
Reading List Christensen, B.L. (1997). Experimental Methodology (7th ed.). Boston: Allyn & Bacon. (p. 229-256) Dr. Margaret Amankwah-Poku Slide 5
Topic One WHAT ARE EXTRANEOUS VARIABLES? Dr. Margaret Amankwah-Poku Slide 6
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 Dr. Margaret Amankwah-Poku Slide 7
What are Extraneous variables? 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
What are Extraneous variables? That is: Experimenter variables Participants variables Environmental variables Measurement variables Dr. Margaret Amankwah-Poku Slide 9
Extraneous Variables Types of extraneous variables 1. General extraneous variables 2. Participants effect 3. Experimenter effect Dr. Margaret Amankwah-Poku Slide 10
Topic Two GENERAL EXTRANEOUS VARIABLES Dr. Margaret Amankwah-Poku Slide 11
General extraneous variables Campbell & Stanley (1963) identified six general sources of extraneous variables that act as threats to internal validity Dr. Margaret Amankwah-Poku Slide 12
General extraneous variables 1. History 2. Maturation 3. Instrumentation 4. Statistical regression 5. Selection Bias 6. Mortality / Attrition Dr. Margaret Amankwah-Poku Slide 13
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 Dr. Margaret Amankwah-Poku Slide 14
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) Dr. Margaret Amankwah-Poku Slide 15
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. Dr. Margaret Amankwah-Poku Slide 16
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 Dr. Margaret Amankwah-Poku Slide 17
2. Maturation Example: Effect of anger management on violent secondary school children If aggressive behaviour decreases, can we conclude that treatment has been effective? Maturation effect: between observations, participants could have grown out of their aggressive behaviour Dr. Margaret Amankwah-Poku Slide 18
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 Dr. Margaret Amankwah-Poku Slide 19
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 Dr. Margaret Amankwah-Poku Slide 20
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 Dr. Margaret Amankwah-Poku Slide 21
3. Instrumentation Example: Effect of anger management on violent secondary school students If aggressive behaviour decreases, can we conclude that treatment has been effective? Testing effect: the act of assessing aggression may have led to awareness of students own aggression Dr. Margaret Amankwah-Poku Slide 22
4. Statistical Regression This is the lowering of extremely high scores or the raising of extremely low scores during posttesting This may occur because participant were selected for a study due to their extremely high or extremely low score on some characteristics Dr. Margaret Amankwah-Poku Slide 23
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 Dr. Margaret Amankwah-Poku Slide 24
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 Dr. Margaret Amankwah-Poku Slide 25
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 Dr. Margaret Amankwah-Poku Slide 26
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 Dr. Margaret Amankwah-Poku Slide 27
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 Dr. Margaret Amankwah-Poku Slide 28
Topic Three PARTICIPANT EFFECTS Dr. Margaret Amankwah-Poku Slide 29
Participant effect Examples of participant effect as extraneous variables are Demand characteristic Good participants tendency Evaluation apprehension Negative attitude Dr. Margaret Amankwah-Poku Slide 30
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 Dr. Margaret Amankwah-Poku Slide 31
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) Dr. Margaret Amankwah-Poku Slide 32
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) Dr. Margaret Amankwah-Poku Slide 33
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 Dr. Margaret Amankwah-Poku Slide 34
Topic Four EXPERIMENTER EFFECTS Dr. Margaret Amankwah-Poku Slide 35
Experimenter Effect Any change in participants performance that can be attributed to the experimenter It includes Experimenter attribute Experimenter expectancies Dr. Margaret Amankwah-Poku Slide 36
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 Dr. Margaret Amankwah-Poku Slide 37
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 Dr. Margaret Amankwah-Poku Slide 38
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 Dr. Margaret Amankwah-Poku Slide 39
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. Dr. Margaret Amankwah-Poku Slide 41