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Get out homework and discuss with neighbor. Be prepared with any questions you might have.

Get out homework and discuss with neighbor. Be prepared with any questions you might have. Get out materials for notes. Designing Experiments, cont. Section 5.2 . Cautions About Experimentation.

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Get out homework and discuss with neighbor. Be prepared with any questions you might have.

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  1. Get out homework and discuss with neighbor. • Be prepared with any questions you might have. • Get out materials for notes.

  2. Designing Experiments, cont. Section 5.2

  3. Cautions About Experimentation • A Randomized Comparative Experiment depends on our ability to treat all the experimental units identically in every way EXCEPT the actual treatments being compared.

  4. Cautions About Experimentation • Attention to detail • How can you ensure that every unit receives exactly the same treatment? • Physicians’ Health Study from yesterday

  5. Cautions About Experimentation • Double-blind experiment • Neither the subjects nor the people observing the response know which treatment a subject received What are some examples of an experiment that can’t be blind? Double-blind?

  6. Examples • http://articles.latimes.com/2011/may/09/health/la-he-unreal-greys-anatomy-20110509 • http://www.thealzcenter.com/trials/

  7. Cautions About Experimentation • Lack of realism • Setting, treatment, or subjects may not realistically duplicate the conditions we want to study • Limits our ability to apply the conclusions of an experiment to the settings of greatest interest. Read Examples 5.14 & 5.15 on p. 300

  8. Cautions About Experimentation • Completely randomized designs are simple but often not as good as more sophisticated designs

  9. Cautions About Experimentation • Matched pairs design • Compares two treatments together in pairs • Each individual gets BOTH treatments • Must randomize the order that treatments are given • An example of block design Read example 5.16 p. 301

  10. Cautions About Experimentation • Block design • Block – a group of units (subjects) that are known to be similar in a way that’s expected to affect response to treatment • Read example 5.17 p. 302 • Random assignment to each treatment is carried out separately within each block

  11. Example • Read Example 5.17, 5.18, & 5.19 p. 302 & 303

  12. Diagrams of Designs Random Assignment testing two treatments Treatment 1 Group 1 Compare Results Random Assignment Treatment 2 Group 2 Random Assignment testing three treatments Treatment 1 Group 1 Compare Results Random Assignment Treatment 2 Group 2 Group 3 Treatment 3

  13. Diagrams of Designs Block Design Treatment 1 Block 1 Compare Results Treatment 2 Treatment 1 Subjects Block 2 Compare Results Treatment 2 Treatment 1 Block 3 Compare Results Treatment 2

  14. Homework • Exercises 5.43, 5.44, 5.45

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