Chapter 8 Experimental Research Experiments Appropriate Technique Confounding

Chapter 8 Experimental Research

Experiments • Appropriate Technique? – Confounding variables • A Short History of the Experiment • Experiments and Theory • Experimental and Survey Methods to Test and Apply Identity Theory 2

Figure 8. 1: Random Assignment and Random Sampling 3

Figure 8. 2: How to Randomly Assign 5

Random Assignment • • • 4 Within-participants Within-groups Between-groups Unbiased Matching versus Random Assignment

Experimental Design Logic • The Language of Experiments – Parts of the Experiment • • • 6 Treatment Dependent variables Pretest Posttest Experimental group

Experimental Design Logic • Control group • Random assignment – Steps in Conducting an Experiment – Control in Experiments • Deception • Confederates • Cover story 7

Experimental Design Logic • Types of Design – Experimental design – Classical Experimental Design – Preexperimental Designs • One-Shot Case-Study Design • One-Group Pretest–Posttest Design • Static Group Comparison 8

Experimental Design Logic – Quasi-Experimental and Special Designs • • • Two-Group Posttest-Only Design Interrupted Time Series Equivalent Time Series Solomon Four-Group Design Factorial Designs • Design Notation 9

Table 8. 1: A Comparison of the Classical Experimental Design 10

Table 8. 2: Summary of Experiment Designs with Notation 12

Internal and External Validity • The Logic of Internal Validity • Threats to Internal Validity – Selection bias – History – Maturation – Testing – Instrumentation 13

Internal and External Validity – Mortality – Statistical regression – Diffusion of treatment – Compensatory Behavior – Experimenter Expectancy – Demand Characteristics – Placebo effect 14

Figure 8. 4: Double-Blind Experiment 15

Internal and External Validity • External Validity – Population Generalization • Field Experiments 17

Figure 8. 5: Three Types of External Validity Generalization 18

Practical Considerations • Planning and Pilot-Tests • Instructions to Participants • Postexperiment Interviews – Debrief • Experimental Results: Making Comparisons • A Word on Ethics 19

Figure 8. 6: Comparisons of Results, Classical Experimental Design, and Weight-Loss Experiments 20