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

Designing Experiments, cont.

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.

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

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?

 th/la-he-unreal-greys-anatomy th/la-he-unreal-greys-anatomy  Examples

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

Cautions About Experimentation  Completely randomized designs are simple but often not as good as more sophisticated designs

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

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

Example  Read Example 5.17, 5.18, & 5.19 p. 302 & 303

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

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

Homework  Exercises 5.43, 5.44, 5.45