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Chapter 11

Chapter 11. Experimental and Quasi-experimental Designs Dr. Bill Bauer. Key Ideas. History of experimental resign Key characteristics of experimental design Types of experimental design Steps in conducting experimental research Criteria for evaluating experimental research.

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Chapter 11

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  1. Chapter 11 Experimental and Quasi-experimental Designs Dr. Bill Bauer l

  2. Key Ideas • History of experimental resign • Key characteristics of experimental design • Types of experimental design • Steps in conducting experimental research • Criteria for evaluating experimental research l

  3. A Brief History of Experimental Designs • Schuyler 1903: control groups • McCall 1916: randomly selected groups • McCall 1925: book on experiments • Fisher 1936: statistical methods book l

  4. A Brief History of Experimental Designs • Campbell and Stanley 1963: 15 types of experimental designs evaluated in terms of threats to validity • Cook and Campbell 1979: four types of validity • 1980 and beyond: computer enhancements to experimental design2 l

  5. Key Characteristics of Experimental Designs • Participants selected and assigned to groups • control • experimental • An intervention is applied to one or more groups • Outcomes are measured at the end of the experiment l

  6. Key Characteristics of Experimental Designs • Procedures are designed that address potential threats to validity • Internal • External • Construct • Statistical Conclusion • Statistical comparisons of different groups are conducted l

  7. Selecting Participants and Assigning Them to Treatments • Decide on the experimental unit of analysis to be treated • individual • group or groups • organization • Randomly assign individuals to groups control for extraneous characteristics that might influence the outcome l

  8. Selecting Participants and Assigning Them to Treatments • Control for extraneous factors • random assignment (equating groups) • pretest/posttest • covariates • matching participants • selecting homogenous samples • using blocking variables l

  9. Controlling for Covariates Independent Variable No Covariates Dependent Variable Covariate Introduced Independent Variable: Type of Instruction Dependent Variable: Rates of Smoking Covariate: Parents Who Smoke Variance Removed Variance l

  10. Matching Process Based on Gender John Jim James Josh Jackson Jane Johanna Julie Jean Jeb Experimental Group Control Group l

  11. Applying an Intervention or Treatment • Identify a treatment variable • identify the conditions or levels of the variable • Manipulate the treatment conditions l

  12. Independent Variables 1. Age (can’t manipulate) 2. Gender (can’t manipulate) 3. Types of Instruction (can manipulate) a. Lecture (control) b. Lecture + Hazard Instruction (Comparison) c. Lecture + Hazard Instruction + slides of damaged lungs (experiment) Dependent Variable Frequency of Smoking The Experimental Manipulation of a Treatment Group l

  13. Threats to Statistical Conclusion Validity • Low statistical power due to low sample size • Violation of assumptions of statistical tests • Use of unreliable measures l

  14. Threats to Internal Validity • History • Maturation • Regression • Selection • Mortality • Interactions with selection l

  15. Threats to Internal Validity • Diffusion of treatments • Compensatory equalization • Compensation rivalry • Resentful demoralization • Testing • Instrumentation l

  16. Threats to Construct Validity • Lack of good operational definitions • Apprehensiveness by participants • Participants “guessing” what the researcher hopes to find l

  17. Threats to External Validity • Interaction of selection and treatment • Interaction of setting and treatment • interaction of history and treatment l

  18. Treatment Comparisons in an Experiment Phase 1: Relationship Picture + Error Correction Treatment Spelling Accuracy Phase 2: Timeline Picture Test 1 Test 2 Test 3 6 Weeks 6 Weeks 6 Weeks 6 Weeks 6 Weeks 6 Weeks Class A: Regular Spelling Practice (Control) Class B: Reduced word list (Comparison) Error Correction Treatment 6 Weeks 6 Weeks 6 Weeks Class C: Error Correction(Experimental) Phase 3: Statistical Comparisons Class A Class B Class C F-value 10.3 (3.6) 10.8 (4.3) 9.9 (3.9) Test 1 Test 2 Test3 0.27 10.6 (3.8) 13.9 (4.2) 10.7 (3.3) 4.90* * p<.05 11.1 (3.3) 10.3 (3.6) 13.1 (3.8) 3.31* l

  19. Types of Experimental Designs: Between Groups • True Experiments • Pre- and posttest • Posttest Only • Quasi Experiments • Pre- and posttest • Posttest Only • Factorial Designs l

  20. Types of Experimental Designs: Within-Group or Individual • Time series experiments • interrupted • uninterrupted • Repeated measures experiments • Single-subject experiments • A/B design • Multiple baseline design • Alternating treatments l

  21. Means and Main Effects of Eight groups in Factorial Design Depression Medium High Low Mean rate of smoking Mean rate of smoking Mean rate of smoking Health lecture Main Effects of Type of Instruction Type of Instruction Mean rate of smoking Mean rate of smoking Mean rate of smoking Standard lecture Main Effects of Depression l

  22. High High High Low Low Low Medium Medium Medium High High High Low Low Low Graphs Showing Main and Interaction Effects Standard lecture (a) No interaction Effects (Parallel) Health lecture Extent of Smoking (b) Interaction Effects (Crossed) (a) Interaction Effects (Crossed) Standard lecture Extent of Smoking Health lecture (c) Interaction Effects (Not Parallel) Standard lecture Extent of Smoking Health lecture l

  23. Steps in Conducting Experimental Research • Decide if an experiment addresses the research problem • Form hypotheses to test cause-effect relationships • Select an experimental treatment and introduce it • Identify study participants l

  24. Steps in Conducting Experimental Research • Choose a type of experimental design • Conduct the experiment • Organize and analyze the data • Develop an experimental research report l

  25. Criteria for Evaluating Experimental Research • Does the experiment have a powerful intervention? • Does it employ few treatment groups (e.g. only two)? • Will participant profit from the intervention? • Is there a systematic way the researcher derived the number of participants per group? l

  26. Criteria for Evaluating Experimental Research • Were there an adequate number of participants used in the study? • Were valid, reliable, and sensitive measures or observations used? • Did the study control for extraneous factors? • Did the researcher control for threats to internal validity? l

  27. Applying What you Have Learned: An Experimental Study Review the article and look for the following: • The research problem and use of quantitative research • Use of the literature • The purpose statement and research hypothesis • Types and procedures of data collection • Types and procedures of data analysis and interpretation • The overall report structure l

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