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Experimental Designs Dr. Farzin Madjidi Pepperdine University Graduate School of Education and Psychology.

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Presentation on theme: "Experimental Designs Dr. Farzin Madjidi Pepperdine University Graduate School of Education and Psychology."— Presentation transcript:


2 Experimental Designs Dr. Farzin Madjidi Pepperdine University Graduate School of Education and Psychology

3 2 2 Experimental Research 4 Researcher looks for cause-and-effect relationships 4 In non-experimental research, the researcher has no control over what has or will happen to the subjects that may affect their response to the dependent variable (treatment). 4 In experimental research, the researcher can control most of these factors

4 3 3 Experimental Research Types of Control The researcher has two types of control: 4 Direct manipulation over of the independent variable by controlling dosages of the treatment (e.g., one group receives the treatment while one doesn’t). 4 Control over extraneous variables by either keeping constant conditions and events except for the independent variable, or by eliminating them

5 4 4 Experimental Designs 4 Single-Group Designs 4 Nonequivalent-Groups 4 Randomized-Groups 4 Factorial Designs 4 Single-Subject Designs

6 5 5 Conventions 4 Most experimental designs are shown graphically 4 Letters A,B,C,D are used to represent groups 4 Letter “O” indicates testing/measurements 4 Letter “X” indicates intervention/treatment 4 Letter “R” indicates the subjects were randomly selected/assigned

7 6 6 Single-Group Designs Posttest-Only Designs (pre-experimental) – Inadequate control over extraneous variables Group Treatment Posttest A X O – Weakest of experimental designs – Applied when the researchers has reasons to believe pre-intervention factors are benign

8 7 7 Single-Group Designs Pretest-Posttest Designs 4 Subjects are tested before the intervention Group Pretest Intervention Posttest A O X O 4 No control over extraneous variables 4 No control/comparison group

9 8 8 Non-Equivalent Groups Posttest Only Designs 4 A control/comparison group is added A X O B O 4 No pre-testing to account for initial differences among subjects

10 9 9 Non-Equivalent Groups Pretest-Posttest Design (Quasi-Experimental) – Best used with existing, intact groups of subjects A O X O B O O Or, A O X1 O B O X2 O

11 10 Randomized-Groups Posttest Only 4 Subjects randomly assigned to each group R A X O B O Or, R A X1 O B X2 O

12 11 Randomized-Groups Pretest-Posttest Only Designs 4 Subjects randomly assigned to each group, before or after pretesting 4 R A O X O B O O Or, R A O X1 O B O X2 O

13 12 Factorial Designs 4 When more than one independent variable is tested Method A Method B Males Group 1 Group 2 Females Group 3 Group 4

14 13 Factorial Designs Males R A O X O B O O Females R A O X1 O B O X2 O 4 You can replicate any of these designs with more than two groups and more than two interventions

15 14 Experimental Designs Key Issues: 4 Primary purpose is to test causal hypothesis 4 Direct manipulation of the Independent Variable 4 Clearly identify the design used 4 Maximize the control of extraneous variables 4 Treatment should be sufficiently different

16 15 Single Subject Designs Studies individuals, or individual cases – Involves multiple measures of behavior – Looks for patterns of behavior – Requires a “reliable” measurement instrument – Requires clear descriptions of the conditions of measurement and nature of treatment – Requires at least one baseline and one treatment as a frame of reference – Single variable rule of change

17 16 Single Subject Designs A-B-A Designs – Requires multiple measurements as follows Baseline Treatment XXXXXX OOOOOOOOOOOOOOOOO Or, Baseline Treatment Baseline XXXXXXX OOOOOOOOOOOOOOOOOOOOOOOOOO – Also called A-B-A design with withdrawal – Multiple-Baseline Designs

18 17 Single Subject Design Key Issues 4 Clear definition of target behavior 4 Reliable measurement of target behavior 4 Clear, full description of procedures, subjects and setting 4 Control experimenter/observer effect 4 Practical significance of results

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