PYSC 224 Introduction to Experimental Psychology

Transcription

1 PYSC 224 Introduction to Experimental Psychology Session 8 Controlling 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/ /2017

2 Session Overview The time to be concerned with internal validity is during the design phase of a study Discovering problems with internal validity after you have conducted an experiment is too late Extraneous variables cause fluctuations in scores that have nothing to do with the effect of the independent variable A poorly designed experiment cannot be fixed later on and therefore it is necessary that during the design phase of an experiment an experimenter is aware of possible extraneous variables and controls for them

3 Session Goals and Objectives At the end of this session, you should be able to Explain why control of extraneous variables is important in experimentation Discuss the three basic techniques for controlling extraneous variables Describe the various ways in which participant effects can be controlled Describe the various ways in which experimenter effects can be controlled Dr. Margaret Amankwah-Poku Slide 3

4 Session Outline The key topics to be covered in the session are as follows: Basic control techniques Controlling participant effects Controlling experimenter effects

5 Reading List Christensen, B.L. (1997). Experimental Methodology (7th ed.). Boston: Allyn & Bacon. (p ) Christensen, B.L. (2007). Experimental Methodology (10th ed.). Boston: Allyn & Bacon. (p )

6 Topic One BASIC CONTROL TECHNIQUES

7 Basic Control Techniques Discovering problems with internal validity after you have conducted a study is too late A poor design study cannot be fixed later on Thus, controlling extraneous variables is very important in experimentation

8 Basic Control Techniques 1. Randomization This technique equates groups of participants by ensuring every member an equal chance of being assigned to any group (Christensen, 2007, pg. 264) It is the most important and basic of all the control methods The only technique for controlling unknown sources of variation It allows internal validity to be established

9 Basic Control Techniques 2. Matching Using one of a variety of techniques to equate participants on one or more variables (Christensen, 2007) Variables on which participants are matched are controlled because constancy of influence is attained Matching can be done in various ways

10 Basic Control Techniques Matching can be done by a. holding variables constant The experimenter controls for extraneous variable(s) by holding them constant for all groups Thus, participants in all the group will have the same degree or type of extraneous variable Example- When studying the effect of group cohesion on conformity, gender needs to be controlled

11 Basic Control Techniques Matching can also be done by b. building the extraneous variables into the research design E.g.- IQ have ranges such as Exptal Group 1- IQ of , Exptal Group etc. Or age years, years, years etc. c. equating participants on the extraneous variable such as IQ, age, gender etc. E.g.-Grouping the participants according to age then randomly assign them to the groups

12 Basic Control Techniques 3. Counterbalancing Used to control sequencing effects When participants in an experiment serve in each of the several experimental conditions sequencing effects can occur The various treatments of the experiment are assigned in a different order for different participants to reduce the sequencing effect Can be complete counterbalancing or partial counterbalancing

13 Basic Control Techniques Complete counterbalancing provides every possible ordering of treatment and assigns at least one subject to each ordering It is practical for experiments with a small number of treatments Example- Six participants who are receiving 3 levels of an independent variable

14 Basic Control Techniques Subjects Treatment Order 1 1, 2, 3 2 1, 3, 2 3 2, 1, 3 4 2, 3, 1 5 3, 1, 2 6 3, 2, 1

15 Basic Control Techniques Partial/ incomplete counterbalancingdifferent groups of participant receive the possible ordering E.g- 36 participants who are receiving 3 levels of an independent variable put into 6 groups to receive each of the ordering of the independent variables

16 Basic Control Techniques Partial Subjects Balancing Treatment Order 1,2,3,4 1, 2, 3 5,6,7,8 1, 3, 2 9,10,11,12 2, 1, 3 13,14,15,16 2, 3, 1 17,18,19,20 3, 1, 2 21,22,23,24 3, 2, 1

17 Basic Control Techniques Two order to administer questionnaires Subjects Treatment Order , , 1

18 Topic Two CONTROLLING PARTICIPANT EFFECTS

19 Controlling participant effects 1. Test Unwitting participants Participants would not know that they are being observed for an experiment They will not be aware that they are in a study and will not alter their behaviour E.g- observing consumer behaviour in a supermarket using a hidden camera or how bystanders will hold an individual who falls to the ground

20 Controlling participant effects 2. Deception Participants think that the experiment is studying one thing when in fact it is studying something else The experimenter provides participants with a hypothesis that is unrelated to the real hypothesis of study E.g.- studying healthy eating among students to determine eating pattern of obese and normal weight students

21 Controlling participant effects 3. Double Blind technique Neither the experimenter nor the participants is aware of the treatment condition administered to the participants Keeps the experimenter from unconsciously influencing participants Someone else administers the treatment (e.g. pills) so the experimenter does not know who was administered what

22 Controlling participant effects The experimenter develop manipulations that look identical to participants in all conditions Both the experimenter and participants do not know which group received the placebo condition or the treatment

23 Controlling participant effects 2. Single blind technique Participants do not know to which group they have been assigned They may know about the goal of the experiment, but do not know which group they are in

24 Topic Three CONTROLLING EXPERIMENTER EFFECTS

25 Controlling Experimenter Effects 1. Use well-trained experimenters Use well-trained experimenters in order to control experimenter effects Train experimenters to behave consistently with all participants irrespective of the group they are in

26 Controlling Experimenter Effects 2. Control of recording errors Misrecording of data can be minimized if the observer remains aware of the necessity to making careful observations in order to obtain accurate data Multiple observers or data recorders could also be used

27 Controlling Experimenter Effects 3. Automation Where possible instructions given to participants can be automated as well as the recording of their responses, for consistency 4. Use the double blind technique Refer to slide 20 & 21

28 Controlling Experimenter Effects 5.Controlling experimenter attributes Use the same experimenter in all the conditions E.g.- To avoid having a friendly experimenter for one group and an unfriendly experimenter for another group

29 END OF SESSION 8

30 References Christensen, B.L. (2007). Experimental Methodology (10th ed.). Boston: Allyn & Bacon. (p , , )