PYSC 224 Introduction to Experimental Psychology

Transcription

1 PYSC 224 Introduction to Experimental Psychology Session 6 Quasi Experiments and Faulty Experimental Designs Part 1 & 2 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 Two other kinds of experimental research design exist; quasi experimental design and faulty experimental design Quasi experimental designs are similar to true experimental designs but in quasi experiments, the experimenter lacks the degree of control over the conditions that is possible in a true experiment Some research studies may necessitate the use of quasi designs rather than true experimental designs Faulty experimental design on the other hand are designs which you should avoid when doing research. They either do not include a control group and/ a pretest Dr. Margaret Amankwah-Poku Slide 2

3 Session Goals and Objectives At the end of this session, you should be able to Define a quasi experiment and distinguish it from a true experiment Determine when to use a quasi design Outline the types of quasi experimental design Define what a faulty experimental design is and distinguish it from a true experiment Outline the types of a faulty experimental designs Dr. Margaret Amankwah-Poku Slide 3

4 Session Outline The key topics to be covered in the session are as follows: Quasi Experimental Designs Faulty Experimental Designs Dr. Margaret Amankwah-Poku Slide 4

5 Reading List Christensen, B.L. (2007). Experimental Methodology (10th ed.). Boston: Allyn & Bacon. (p ) Kantowitz, B. H., Roediger III, H. L., Elmes, D. G. (2015). Experimental Psychology. Stamford: Cengage Learning (Pp 81) Dr. Margaret Amankwah-Poku Slide 5

6 Topic One QUASI EXPERIMENTAL DESIGN Dr. Margaret Amankwah-Poku Slide 6

7 Quasi Experiments Quasi means as if or to a degree (McBurney (2001) Quasi experiment- an experiment that does not meet all the requirements necessary for controlling the influence of extraneous variable (Christensen, 2007, p. 330) Dr. Margaret Amankwah-Poku Slide 7

8 Quasi Experiment Participant variables such as age, sex, etc. cannot be experimentally manipulated Participants cannot be randomly assigned to a particular condition Instead they are exposed to a condition because they already qualify for that condition Dr. Margaret Amankwah-Poku Slide 8

9 Quasi Experiment The experimenter can only select instances that satisfy different categories and study them Use natural manipulations rather than manipulations by the researcher Manipulation could be naturally occurring attribute or events- e.g. ethnic group, age, sex, intelligence etc. Dr. Margaret Amankwah-Poku Slide 9

10 Quasi Experiment Sometimes called ex post facto or after the fact experiments The experiment is conducted after the groups have been formed The inability to control confounding variables reduces the internal validity of a quasi experiment but does not make it invalid Dr. Margaret Amankwah-Poku Slide 10

11 Quasi Experiment Note that it is possible to have one experimental variable and one quasi variable in one experiment Example- investigating the effect of practice on performance will require a true experimental design The effect of practice and gender on performance will require a combination of a true and quasi experiment Dr. Margaret Amankwah-Poku Slide 11

12 Quasi Experiments Difference between true experiment and quasi experiments Major difference- random assignment of participant to experimental groups in true experiments but not quasi experiments Experimenter manipulates variables in true experiments but observes categories of participants in quasi experiments Dr. Margaret Amankwah-Poku Slide 12

13 Quasi Experiments True experiments- Control permits the establishment of cause effect relationship Quasi experiment- cannot be determined whether difference in behaviour is caused by the independent variable or the difference between the two groups Generally, true experiments are preferred to a quasi experiment Dr. Margaret Amankwah-Poku Slide 13

14 Topic Two TYPES OF QUASI EXPERIMENTAL DESIGNS Dr. Margaret Amankwah-Poku Slide 14

15 Quasi Experimental Designs Two types of quasi experimental designs 1. Non-equivalent control group design 2. Non-equivalent Pretest-posttest design Dr. Margaret Amankwah-Poku Slide 15

16 1. Non-equivalent control group design The performance of an experimental group is compared with that of a non-equivalent control group There is no random assignment of subjects so the groups are not equivalent Dr. Margaret Amankwah-Poku Slide 16

17 1. Non-equivalent control group design Thus, difference between the groups becomes a confounding variable This provides an alternative explanation for the results obtained Testing non-equivalent groups of participants creates selection difference Dr. Margaret Amankwah-Poku Slide 17

18 1. Non-equivalent control group design Effect of stress management on hypertensive patients Experimental Group Independent Variable Measure Dependent Variable Non-equivalent Control Group No Independent Variable Measure Dependent Variable Dr. Margaret Amankwah-Poku Slide 18

19 1. Non-equivalent control group design Example-The effect of stress management on hypertensive patients An experimenter may recruit willing hypertensive patients who serve as the experimental group and are administered stress management The experimenter later recruits more hypertensive patients to serve as the control group Dr. Margaret Amankwah-Poku Slide 19

20 1. Non-equivalent control group design Thus, the two groups are not equated Differences found between the two groups, may be as a result of the stress management or difference between the two groups This design is similar to the true experiment posttest-only Dr. Margaret Amankwah-Poku Slide 20

21 2. Non-equivalent pretest- posttest design An experimental and control group are pretested and posttested However, the two groups are not equivalent Differences between the groups, may be as a result of the initial difference or the effect of the independent variable Dr. Margaret Amankwah-Poku Slide 21

22 2. Non-equivalent pretest- posttest design Effect of stress management on diabetes control Experimental Group Pretest: Measure Dependent Variable Administer Independent Variable Posttest: Measure Dependent Variable Non-equivalent Control Group Pretest: Measure Dependent Variable No Independent Variable Posttest: Measure Dependent Variable Dr. Margaret Amankwah-Poku Slide 22

23 2. Non-equivalent pretest- posttest design Experimental Group Pretest Score 70% Stress Management Posttest Score 30% Control Group Pretest Score 40% No Stress Management Posttest Score 35% Dr. Margaret Amankwah-Poku Slide 23

24 Topic Three FAULTY EXPERIMENTAL DESIGNS Dr. Margaret Amankwah-Poku Slide 24

25 Faulty Experiment Faulty experimental designs usually do not have a control group or do not include a pretest There is internal invalidity as a result of not minimizing extraneous variables They should therefore be avoided by researchers Dr. Margaret Amankwah-Poku Slide 25

26 Faulty Experiment Two types of faulty research designs 1. One group posttest-only design 2. One group pretest-posttest design Dr. Margaret Amankwah-Poku Slide 26

27 1. One group posttest-only design An experimental group is administered the independent variable and then tested on the dependent variable There is no comparison group or pretest measure At a minimum, participants should be pretested Also, an equivalent control group must be included Dr. Margaret Amankwah-Poku Slide 27

28 1. One group posttest-only design The effect of type of Music on Mood Experimental Group Independent Variable (listen to music) Posttest: Measure Dependent Variable (Mood) Dr. Margaret Amankwah-Poku Slide 28

29 2. One-group pretest-posttest design The effect of an independent variable is inferred from the pretest-posttest differences in a single group This design is faulty because it does not take into account extraneous variables such as history, maturation, etc. Also, there is no control group to compare the experimental group with Dr. Margaret Amankwah-Poku Slide 29

30 2. One group pretest-posttest design Effect of stress management on diabetes control Experimental Group Pretest: Measure Dependent Variable Administer Independent Variable Posttest: Measure Dependent Variable Dr. Margaret Amankwah-Poku Slide 30

31 One-Group pretest-posttest design Example- A block manufacturing factory decides to change their work schedule from 8 hours a day to 10 hours a day If there is improvement in productivity it does not definitely mean this is because of the increase in the number of hours Other potential causes such as favourable weather condition, attention paid to employees when the change was initiated etc. can also increase productivity Dr. Margaret Amankwah-Poku Slide 31

32 END OF SESSION 6 Part 1 & 2

33 References Christensen, B.L. (2007). Experimental Methodology (10th ed.). Boston: Allyn & Bacon. (p , , ) Dr. Margaret Amankwah-Poku Slide 33