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Chapter 11

Chapter 11 . Experimental Designs. Key Ideas. Definition and uses for experimental designs Procedures used in experimental research Internal and external validity threats in experimental research Types of experimental designs Steps in conducting experimental research

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Chapter 11

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  1. Chapter 11 Experimental Designs Power Point Slides by Ronald J. Shope in collaboration with John W. Creswell

  2. Key Ideas • Definition and uses for experimental designs • Procedures used in experimental research • Internal and external validity threats in experimental research • Types of experimental designs • Steps in conducting experimental research • Evaluating experimental research Educational Research 2e: Creswell

  3. When do you use experimental procedures? • To establish cause and effect • Between independent and dependent variables • Control for all variables that might influence the outcome • Used when testing theories • Used when comparing two or more groups Educational Research 2e: Creswell

  4. Key Characteristics of Experimental Designs • Random assignment • Control over extraneous variables • Manipulation of the treatment conditions • Outcome Measures • Group Comparisons • Threats to validity Educational Research 2e: Creswell

  5. Phase 1: Relationship Picture Spelling Accuracy Error Correction Treatment 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) Class C: Error Correction (Experimental) Error Correction Treatment 6 Weeks 6 Weeks 6 Weeks Phase 3: Statistical Comparisons Class A Class B Class C F-value 10.3 (3.6) 10.8 (4.3) 9.9 (3.9) 0.27 Test 1 Test 2 Test3 10.6 (3.8) 13.9 (4.2) 10.7 (3.3) 4.90* 11.1 (3.3) 10.3 (3.6) 13.1 (3.8) 3.31* Group comparisons in an experiment + * p<.05 Educational Research 2e: Creswell

  6. History Maturation Regression Selection Mortality Interactions with selection Diffusion of treatments Compensatory equalization Compensation rivalry Resentful demoralization Testing Instrumentation Threats to internal validity Educational Research 2e: Creswell

  7. Threats to external validity • Interaction of selection and treatment • Interaction of setting and treatment • Interaction of history and treatment Educational Research 2e: Creswell

  8. Types of experiments: Between groups • True Experiments • Pre- and posttest • Posttest Only • Quasi Experiments • Pre • Posttest • Factorial Designs Educational Research 2e: Creswell

  9. 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 Means and Main Effects of Eight groups in Factorial Design Educational Research 2e: Creswell

  10. Types of Experiments: Within-group or individual • Time series experiments • interrupted • uninterrupted • Repeated measures experiments • Single-subject experiments • A/B design • Multiple baseline design • Alternating treatments Educational Research 2e: Creswell

  11. Steps in Conducting Experimental Research • Decide if an experimental design fits research problem • Form cause/effect hypotheses • Select experimental unit and identify study participants • Select an experimental treatment and introduce it • Choose a type of experimental design • Conduct the experiment • Organize and analyze the data • Develop an experimental research report Educational Research 2e: Creswell

  12. Criteria for Evaluating Experimental Research • Does the experiment have a powerful intervention? • Does it employ few treatment groups (e.g. only two)? • Will participant gain from the intervention(s)? • Is there a systematic way the researcher derived the number of participants (cell size)? • Was 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? Educational Research 2e: Creswell

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