1. Chapter 51 Experiments, Good and Bad

2. Chapter 52 Thought Question 1 In studies to determine the relationship between two conditions (activities, traits, etc.), one of them is often defined as the explanatory (independent) variable and the other as the outcome or response (dependent) variable. In an experiment to determine whether the drug memantine improves cognition of patients with moderate to severe Alzheimer’s disease, whether or not the patient received memantine is one variable, and cognitive score is the other. Which is the explanatory variable and which is the response variable?

3. Chapter 53 Thought Question 2 In an observational study, researchers observe what individuals do (or have done) naturally, while in an experiment, they randomly assign the individuals to groups to receive one of several “treatments”. Give an example of a situation where an experiment would not be feasible and thus an observational study would be needed.

4. Chapter 54 Thought Question 3 In testing the effect of memantine on the cognition of Alzheimer’s disease patients (from TQ #1), how would you go about randomizing 100 patients to the two treatment groups (memantine group & placebo group)? Why is it necessary to randomly assign the subjects, rather than having the experimenter decide which patients should get which treatment?

5. Chapter 55 Common Language u Response variable –what is measured as the outcome or result of a study u Explanatory variable –what we think explains or causes changes in the response variable –often determines how subjects are split into groups u Subjects –the individuals that are participating in a study u Treatments –specific experimental conditions (related to the explanatory variable) applied to the subjects

6. Chapter 56 Case Study Quitting Smoking with Nicotine Patches (JAMA, Feb. 23, 1994, pp. 595-600) u Variables: –Explanatory: Treatment assignment –Response: Cessation of smoking (yes/no) u Treatments –Nicotine patch –Control patch u Random assignment of treatments

7. Chapter 57 Case Study Meditation and Aging (Noetic Sciences Review, Summer 1993, p. 28) u Variables: –Explanatory: Observed meditation practice (yes/no) –Response: Level of age-related enzyme u Treatment not randomly assigned.

8. Chapter 58 Randomized Experiment versus Observational Study Both typically have the goal of detecting a relationship between the explanatory and response variables. u Experiment –create differences in the explanatory variable and examine any resulting changes in the response variable u Observational Study –observe differences in the explanatory variable and notice any related differences in the response variable

9. Chapter 59 Why Not Always Use a Randomized Experiment? u Sometimes it is unethical or impossible to assign people to receive a specific treatment. u Certain explanatory variables, such as handedness or gender, are inherent traits and cannot be randomly assigned.

10. Chapter 510 Experiments: Basic Principles u Randomization –to balance out extraneous variables across treatments u Placebo –to control for the power of suggestion u Control group –to understand changes not related to the treatments

11. Chapter 511 Randomization: Case Study Quitting Smoking with Nicotine Patches (JAMA, Feb. 23, 1994, pp. 595-600) u Variables: –Explanatory: Treatment assignment –Response: Cessation of smoking (yes/no) u Treatments –Nicotine patch –Control patch u Random assignment of treatments

12. Chapter 512 Placebo: Case Study Quitting Smoking with Nicotine Patches (JAMA, Feb. 23, 1994, pp. 595-600) u Variables: –Explanatory: Treatment assignment –Response: Cessation of smoking (yes/no) u Treatments –Nicotine patch –Placebo: Control patch u Random assignment of treatments

13. Chapter 513 Control Group: Case Study Mozart, Relaxation and Performance on Spatial Tasks (Nature, Oct. 14, 1993, p. 611) u Variables: –Explanatory: Relaxation condition assignment –Response: Stanford-Binet IQ measure u Active treatment: Listening to Mozart u Control groups: –Listening to relaxation tape to lower blood pressure –Silence

14. Chapter 514 Confounding (Lurking) Variables u The problem: –in addition to the explanatory variable of interest, there may be other variables that make the groups being studied different from each other –the impact of these variables cannot be separated from the impact of the explanatory variable on the response

15. Chapter 515 Confounding (Lurking) Variables u The solution: –Experiment: randomize experimental units to receive different treatments (possible confounding variables should “even out” across groups) –Observational Study: measure potential confounding variables and determine if they have an impact on the response (may then adjust for these variables in the statistical analysis)

16. Chapter 516 Confounding Variables: Case Study Heart or Hypothalamus? (Scientific American, May 1973, pp. 26-29) u Infants were not randomized to either hear the heartbeat sound or not u Same nursery was used on subsequent days with different groups of babies u Environment variables –construction noise –temperature

17. Chapter 517 Statistical Significance u If an experiment or observational study finds a difference in two (or more) groups, is this difference really important? u If the observed difference is larger than what would be expected just by chance, then it is labeled statistically significant. u Rather than relying solely on the label of statistical significance, also look at the actual results to determine if they are practically important.

18. Chapter 518 Key Concepts u Critical evaluation of an experiment or observational study u Common terms –explanatory vs. response variables –treatments, randomization u Randomized experiments –basic principles and terminology –problem with confounding variables