Experiment

1. Experiment Subjecting the sample to a controlled treatment. The objects on which the treatment is imposed on are called subjects. The response variable measures an outcome or result of a study. Explanatory variables explain or cause a change in the response variable. These determine the treatments imposed on the subjects.

2. An experiment with more than 2 treatments: Studying the Durability of Fabric under repeated washings. • What are the explanatory variables? • What is the response variable? • What are the subjects?

3. Completely Randomized Design • Randomly assign a treatment to each experimental unit • The number of units assigned to each treatment is as equal as possible • Randomization is expected to spread any differences among units equally across all treatment groups • Any significant difference in the two groups’ responses can be attributed to treatments used – therefore there are no confounding issues

4. Is weight training good for children? If so, is it better for them to lift heavy weights for a few repetitions or moderate weights a larger number of times? 14--Heavy load group Measure muscular strength & endurance Compare between groups 43 volunteers Randomly assigned to 3 groups 15--Moderate load group 14--Control group – no weights

5. 3 Principles of Good Experimental Design Randomization--randomly assigning subjects to treatment groups Control— comparing two or more treatments Replication--consistency to many subjects

6. Replication When administering the treatments, be consistent with each procedure for each subject/unit. Make sure to use enough subjects to reduce chance variation in the results.

7. Randomization--Crucial “Researchers randomize to reduce the likelihood that the results will be affected by confounding variables and other sources of bias.” Randomize Type of Treatment Randomize Order of Treatment

8. Each subject draws out of a bag a colored chip - each treatment is a different color Each subject is assigned a number - first set of random numbers produced go to one treatment and the rest to the other Each subject rolls a die - odds go to one treatment, evens to the other Each subject flips a coin - heads go one treatment, tails to the other Ways to Randomize

9. What if we didn’t randomize? • Suppose we took volunteers to participate in a study to reduce stress at the workplace • For six weeks, one group took a yoga class, and the other group took a kickboxing class. The volunteers chose the class they would participate in. • If the participants in the yoga classes significantly reduced their stress level, could we say that it was due to the yoga class? • What might be a confounding variable?

10. Control group--receives standard/traditional treatment OR aPlacebo -receives no treatment but subjects believe they are receiving treatment Control Groups are used to control for UNKNOWNvariability! Single Blind:subjects don’t know which treatment they receive Double Blind:subjects and evaluators are “blind”; only the researcher has the “key”

13. Designing a good experiment will: • Reduce the effect of any confounding variables, as they should be evenly spread out among the treatment groups. • Determine cause and effect – any statistically significant differences (so large they would rarely occur by chance) in the response variable can be attributed to the treatments

15. Quitting Smoking w/Nicotine Patches Recruited 240 smokers (volunteers) at Mayo Clinic from 3 large cities Randomly assigned 22-mg nicotine patch or placebo patch for 8 weeks. All attended counseling before, during, and after. Double-blind (neither volunteers nor nurses taking measurements knew type of patch) After 8-wk (1 yr), 46% (27.5%) of nicotine patch group quit smoking and 20% (14.2%) of placebo group quit.

16. Quitting Smoking w/Nicotine Patches • What are the subjects? • What are the treatments? • What was the explanatory variable? • What was the response variable? • How was randomization applied? • How was control applied? • How was replication applied? • Is this an experiment or an observational study? • How would you summarize the results of this experiment?

17. Design the experiment: • A baby-food producer claims that her product is superior to that of her leading competitor, in that babies gain weight faster with her product. 30 healthy babies are available for a clinical trial.

18. Completely Randomized Design • Randomly assign babies to treatments. Have 15 red and 15 blue chips in a bag and draw one for each baby. Reds get her product, blues get the competitor’s product. • Or …Assign each baby a number 01-30. Generate 15 distinct random numbers in this range to get her product. The rest get the competitor’s product. • Compare the weight gain of the babies after the two month period.