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Experimental Design

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

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Experimental Design

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  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 • O = observation (either pre-test or post-test) • X = treatment • = 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) • X1 = experimental treatment • X0 = control condition or comparison treatment

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

  5. Note About the Validity • 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.

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

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

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

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

  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 • Selection • Interaction of selection • history

  15. Design 8: equivalent time samples design X0O X1O X0O X1O Threats to Internal and External Validity: • 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 • Maturation • Instrumentation • Testing • Statistical regression

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

  19. Design 6: static group comparison X O -------- O Threats to Internal and External Validity: • Selection • 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-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

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