1. Experimental Design Presented By: Amber Atwater & Charlott Livingston

2. “When you start in science, you are brainwashed into believing how careful you must be and how difficult it is to discover things. There’s something that might be called the “graduate student syndrome”; graduate students hardly believe they can make a discovery.” ~Francis Crick~

3. Key R = random assignment R = random assignment O = observation (either pre-test or post-test) O = observation (either pre-test or post-test) X = treatment X = treatment = there is not a symbol for a control group so it is represented by a blank = there is not a symbol for a control group so it is represented by a blank ----- = a dotted line between two groups of symbols indicates that the two groups are intact (not random) ----- = a dotted line between two groups of symbols indicates that the two groups are intact (not random) X 1 = experimental treatment X 1 = experimental treatment X 0 = control condition or comparison treatment X 0 = control condition or comparison treatment

4. Scientific Method Choose a topic Choose a topic Identify the problem Identify the problem Research the problem Research the problem Develop a hypothesis Develop a hypothesis Design the Experiments Design the Experiments Test the hypothesis by doing experiments Test the hypothesis by doing experiments Analyze the results Analyze the results Formulate conclusions Formulate conclusions

5. Note About the Validity Threats to internal and external validity that effect the generalization of an experiment Threats to internal and external validity that effect the generalization of an experiment In addition, influences known as confounds, which are sources of confusion, should be minimized. In addition, influences known as confounds, which are sources of confusion, should be minimized.

6. Internal Validity History History Maturation Maturation Instrumentation Instrumentation Testing Testing Statistical Regression Statistical Regression Selection Interaction Selection Interaction

7. External Validity Selection Bias Selection Bias Reactive effects of experimental arrangements Reactive effects of experimental arrangements Reactive effect of testing (pretest sensitization) Reactive effect of testing (pretest sensitization) Multiple treatment interference Multiple treatment interference

8. Basic Experimental Methods True experimental design True experimental design Quasi-experimental design Quasi-experimental design Pre-experimental design Pre-experimental design

9. True Experimental Design There are three true experimental designs

10. Design 1: pre-test post-test randomized control group design R O X O R O O Threats to Internal and External Validity: No known threats No known threats

11. Design 2: post-test only randomized control group design R X O R O Threats to Internal and External Validity: Pretest sensitivity Pretest sensitivity

12. Design 3: Solomon randomized four group design R O X O R O O R X O R O Threats to Internal and External Validity No known threats No known threats

13. Quasi-Experimental Design There are two quasi-experimental designs

14. Design 7: nonequivalent control group design O X O -------- O O Threats to Internal and External Validity: Mortality Mortality Selection Selection Interaction of selection Interaction of selection history history

15. Design 8: equivalent time samples design X 0 O X 1 O X 0 O X 1 O Threats to Internal and External Validity: Multiple treatment interference Multiple treatment interference

16. Pre-Experimental Design There are three pre-experimental designs

17. Design 4: one group pre-test post-test O X O Threats to Internal and External Validity: History History Maturation Maturation Instrumentation Instrumentation Testing Testing Statistical regression Statistical regression

18. Design 5: one-shot case study X O Threats to Internal and External Validity: No pretest = no comparison No pretest = no comparison

19. Design 6: static group comparison X O X O -------- -------- O Threats to Internal and External Validity: Selection Selection No pretest = no comparison No pretest = no comparison

20. Confounds A confound is a source of confusion regarding the explanation for a given difference Hawthorn Effect John Henry Effect Placebo Effect Blind Procedures Double-blind Experiments Demand Characteristics

21. References Campbell, D., & Stanley, J. (1963). Experimental and quasi-experimental designs for research. Dallas: Houghton Mifflin Company. Heffner, C. L. (2004). Research Methods. Retrieved February 13, 2009, from All Psych Online Website: http://allpsych.com/researchmethods/experimentaldesign.html” Key, J. P. (1997). Experimental Research and Design. Retrieved February 13, 2009, from Oklahoma State University Website: http://www.okstate.edu/ag/agedcm4h/academic/aged5980a/5980/newpage2.html Patten, M. L. (2009). Understanding research methods: an overview of the essentials seventh edition. Glendale, CA.: Pyrczak. Sridhar, M. S. (2008). Research Methodology: Part 4 – Experimental Design. Retrieved February 13, 2009, from Scribd Website: http://www.scribd.com/doc/1555464/Research-Methodology-Part-4-Experimental-Designhttp://www.scribd.com/doc/1555464/Research-Methodology-Part-4-Experimental-Design The Scientific Method (n.d.). Retrieved February 13, 2009 from website http://www.biology.ed.ac.uk/research/groups/jdeacon/statistics/tress2.html#DESIGN%20OF%20EXPERIMENTS http://www.biology.ed.ac.uk/research/groups/jdeacon/statistics/tress2.html#DESIGN%20OF%20EXPERIMENTS