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

Educational Research 2e: 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 2e: 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 2e: 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 2e: Creswell Group comparisons in an experiment + * p<.05 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 Class A: Regular Spelling Practice (Control) Class B: Reduced word list (Comparison) Phase 3: Statistical Comparisons Class A Class B Class C F-value Test 1 Test 2 Test (3.6) 10.7 (3.3) 11.1 (3.3) 10.8 (4.3) 10.6 (3.8) 10.3 (3.6) 9.9 (3.9) 13.9 (4.2) 13.1 (3.8) * 3.31* Error Correction Treatment 6 Weeks 6 Weeks 6 Weeks Class C: Error Correction (Experimental )

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

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

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

Educational Research 2e: Creswell 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 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 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?