Chapter 11 Experimental Designs Power Point Slides by

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

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 2 e: Creswell

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 2 e: Creswell

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 2 e: Creswell

Group comparisons in an experiment Phase 1: Relationship Picture + Error Correction Treatment Spelling Accuracy Test 1 Test 2 6 Weeks Phase 2: Timeline Picture Class A: Regular Spelling Practice (Control) Class B: Reduced word list (Comparison) Class C: Error Correction (Experimental) Error Correction Treatment Phase 3: Statistical Comparisons Test 1 Test 2 Test 3 Class A 10. 3 (3. 6) 10. 7 (3. 3) 11. 1 (3. 3) Class B 10. 8 (4. 3) Test 3 6 Weeks Class C F-value 9. 9 0. 27 (3. 9) 10. 6 (3. 8) 13. 9 (4. 2) 4. 90* 10. 3 (3. 6) 13. 1 (3. 8) 3. 31* Educational Research 2 e: Creswell 6 Weeks * p<. 05

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

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

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

Means and Main Effects of Eight groups in Factorial Design Depression Low Health lecture Type of Instruction Standard lecture Medium High Mean rate Mean rate of of of smoking smoking Main Effects of Depression Educational Research 2 e: Creswell Main Effects of Type of Instruction

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

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 2 e: Creswell

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 2 e: Creswell