1. Stat 301 – Day 18 Randomized comparative double-blind experiments

2. Last Time Explanatory variable vs. response variable cursive writing test takersessay scores block print obs.units explanatoryresponse Observational study vs. Experimental study Better educated Less educated Confounding variable

3. Association vs. Causation

4. PP 2.3 (p. 138) A well-designed experiment doesn’t just manipulate something, it actively assigns experimental units to the explanatory variable groups Explanatory variable = positive/negative emotions This was not controlled by the researchers Don’t draw cause-and-effect conclusions about the impact of moods on health from this study

5. How do we form the groups? Investigation 2.4

6. Randomized Experiment Randomizing experimental units to groups should create groups that are similar on all potential confounding variables, even variables that aren’t identified or measured Looking to balance variables across groups rather than being more likely to have the groups systematically differ in some way

7. Best Table in Entire Text

8. Uses of randomness

9. But what if we don’t trust in the random assignment? A randomized block design

10. Investigation 2.5 (p. 143)

11. To Do Finish HW 4  Office hours today 2-4, tonight 8-9, tomorrow 9-10 Watch video(4:16)video Answer questions (a)-(d) for Investigation 2.6 PP 2.4 See Project 2 guidelines